In my test here 1 SELECT instead of 5 (when doing a DAV request,
probably similar for other requests)

Conflicts:
	lib/private/vcategories.php

 - Use camelCase

 - Add some phpdoc

 - Fix some indents

 - Use some more spacing

- Better error messages

- Translate untranslated strings

Basically picks non-app-dependency related stuff from #4017

This way the error won't be fatal in a unit test

introduce pre-disable-app hook and use it for the encryption app to reset migration status if the app was disabled

version checks for apps now use all three version numbers and fixed bug that would not do the version check correctly for the second version

Add support for a reverse proxy that handles multiple domains via different
web roots (http[s]://proxy.tld/domain.tld/owncloud).

As the reverse proxy web root is transparent for the web server the
REQUEST_URI and SCRIPT_NAME need manual adjustments. This patch replace
the direct use of this _SERVER variables with function calls and extend
this functions to overwrite the web root. Additionally it adds a Sabre
request backend that extends the Sabre_HTTP_Request to use the same
functions.

below the standard login a list of icons/button will be displayed