restapi: default version to 'general'

- Added configCommon.defaultConfigurationVersion when querying
for ApplicationMode instead of passing null.
- Added 'default' getConfigurationValue and call it from all
locations that passed a null 'Version' before.

Change-Id: I946c9925f3e0b94a9dad86f0958c2f9e1d0ab5c8
Signed-off-by: Alexander Wels <awels@redhat.com>