Remove implicit conversions

Implicit conversions are something that nlohmann library itself is a bad
default, and 3 years ago threatened to change the default.  These
implicit conversions cause a number of crashes that are hard to
reproduce, because they throw an uncaught exception.

Update the code to be able to do no more implicit conversions.

Tested: Entity-manager launches and runs.  Items are detected correctly
and show up on dbus.  Unit tests pass.

Change-Id: Ib23159ae58f5584641427d9be7545bc25a3619af
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/meson.build b/meson.build
index c364a9e..4df6652 100644
--- a/meson.build
+++ b/meson.build
@@ -6,7 +6,10 @@
     version: '0.1',
     meson_version: '>=1.3.0',
 )
-add_project_arguments('-Wno-psabi', language: 'cpp')
+add_project_arguments(
+    ['-Wno-psabi', '-DJSON_USE_IMPLICIT_CONVERSIONS=0'],
+    language: 'cpp',
+)
 
 boost_args = [
     '-DBOOST_ASIO_NO_DEPRECATED',