Add Configuration class

Adding this class improves maintainability by increasing separation
of concern. One major improvement is the removal of reoccuring calls to
loadConfigurations. These calls took a long time. Now it's only called
once.

Tested:
QEMU/yosemite4 with probe statement set to TRUE.
```
root@yosemite4:~# journalctl | grep entity-manager
Dec 19 13:26:21 yosemite4 entity-manager[502]: Clearing previous configuration
Dec 19 13:26:25 yosemite4 entity-manager[502]: Inventory Added: Yosemite 4 Management Board
root@yosemite4:~# busctl tree xyz.openbmc_project.EntityManager
`- /xyz
  `- /xyz/openbmc_project
    |- /xyz/openbmc_project/EntityManager
    `- /xyz/openbmc_project/inventory
      `- /xyz/openbmc_project/inventory/system
        `- /xyz/openbmc_project/inventory/system/board
          `- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/All_Fan
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P0V6_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P12V_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P1V0_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P1V2_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P1V8_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P2V5_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P3V3_RGM_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P3V3_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P3V_BAT_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P5V_USB_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_ADC_P5V_VOLT_V
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/MGNT_TEMP_C
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/PID_NIC_TEMP
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Stepwise_MGNT_TEMP
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Stepwise_NIC_TEMP
            |- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Stepwise_SENTINEL_DOME_SLOT_PRESENT_PERCENTAGE
            `- /xyz/openbmc_project/inventory/system/board/Yosemite_4_Management_Board/Zone_1
```

Change-Id: I5684a03232012e14d97edcf4ea5ed1aed4d50c8d
Signed-off-by: Christopher Meis <christopher.meis@9elements.com>
diff --git a/src/entity_manager/dbus_interface.hpp b/src/entity_manager/dbus_interface.hpp
index 51d967e..84efec8 100644
--- a/src/entity_manager/dbus_interface.hpp
+++ b/src/entity_manager/dbus_interface.hpp
@@ -69,13 +69,13 @@
                 const std::vector<PropertyType>& newVal,
                 std::vector<PropertyType>& val) {
                 val = newVal;
-                if (!configuration::setJsonFromPointer(jsonPointerString, val,
-                                                       systemConfiguration))
+                if (!setJsonFromPointer(jsonPointerString, val,
+                                        systemConfiguration))
                 {
                     std::cerr << "error setting json field\n";
                     return -1;
                 }
-                if (!configuration::writeJsonFiles(systemConfiguration))
+                if (!writeJsonFiles(systemConfiguration))
                 {
                     std::cerr << "error setting json file\n";
                     return -1;
@@ -103,13 +103,13 @@
          jsonPointerString{std::string(jsonPointerString)}](
             const PropertyType& newVal, PropertyType& val) {
             val = newVal;
-            if (!configuration::setJsonFromPointer(jsonPointerString, val,
-                                                   systemConfiguration))
+            if (!setJsonFromPointer(jsonPointerString, val,
+                                    systemConfiguration))
             {
                 std::cerr << "error setting json field\n";
                 return -1;
             }
-            if (!configuration::writeJsonFiles(systemConfiguration))
+            if (!writeJsonFiles(systemConfiguration))
             {
                 std::cerr << "error setting json file\n";
                 return -1;