Convert OC_Appconfig to object interface

Implemented unittest for OC\AppConfig
check for valid appinfo in installer
Style fixes
Enable appconfig asserts
Merge branch 'master' into convert-oc_appconfig
Move legacy file to correct location
use the 'new' server container for appconfig
Add caching to appconfig
Remove the Test_AppConfig_Object tests as they no longer make sense with caching
Merge branch 'master' into convert-oc_appconfig
Add explicit sorting
sort expected result in tests
Merge pull request #4624 from owncloud/convert-oc_appconfig

Convert OC_Appconfig to object interface