don't allow to share single files with delete permissions, user should only be possible to unshare a single file but never to delete it

The getfile routing code was absolutely legacy and not needed anymore. Additionally \OC::$REQUESTEDAPP was never set to the actually accessed application.

This commit removes the legacy routing code and ensures that $REQUESTEDAPP is always set so that other applications (e.g. the firewall or a two-factor authentication) can intercept the currently accessed app.

Testplan:
[x] Installation works
[x] Login with DB works
[x] Logout works
[x] Login with alternate backend works (tested with user_webdavauth)
[x] Other apps are accessible
[x] Redirect on login works (e.g. index.php?redirect_url=%2Fcore%2Findex.php%2Fsettings%2Fapps%3Finstalled)
[x] Personal settings are accessible
[x] Admin settings are accessible
[x] Sharing files works
[x] DAV works
[x] OC::$REQUESTEDAPP contains the requested application and can be intercepted by other applications

- the file/folder's permission is now stored in the file cache
- BackGroundWatcher has been removed - this has meanwhile be replaced by occ files:scan which can be executed in a cron jobs
- increase version to trigger database migration

This prevents routes like "core/js/oc.js" to automatically load apps and
trigger their update prematurely.

When upgrade, also simulate the database schema update for apps before
doing the actual upgrade.

This includes all mountpoints except the Shared one in
the used space calculation.

Added unit tests for ext storage inclusion in quota calculation

Updating SabreDAV namespaces