Add App-Dependency checks
Fix typos, use \Exception and prohibit deactivati…

vation if other apps depend on the deactivated one
Own exceptions to be more verbose in errormessages
Add OutdatedDependencyException &add/fix unittests
Improve long SQL-clause
Use OC_Appconfig::getValues() instead of own SQL
Small improvements

- Have the dependency check not in an elseif, so following code may be executed

- Add a DISTINCT to depends on check, so nothing is shown multiple times