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
Improve SQLclause & 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

- Have exceptions in own files

- Clean up and translate strings

- Fix SQL, add a comment and remove unnecessary if

- Don't return unneccesary true & use multiple catch

- Add generic error on enable, if there's no message
Improve unittests – Add more assertions