Created sensor cache class

Created sensor cache and sensor interface that needs to be
implemented by sensors.

Tested:
- Sensors created by sensor cache are stored and reused if
  there is try to access same sensor multiple times.
- All other units tests are passing

Change-Id: I552b2016bca4688e1b2a223297587826af256b54
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/meson.build b/meson.build
index 42bd59f..8d0b018 100644
--- a/meson.build
+++ b/meson.build
@@ -67,9 +67,10 @@
     'telemetry',
     [
         'src/main.cpp',
+        'src/persistent_json_storage.cpp',
         'src/report.cpp',
         'src/report_manager.cpp',
-        'src/persistent_json_storage.cpp',
+        'src/sensor_cache.cpp',
     ],
     dependencies: [
         boost,