External storage space is now not counted in total space

Added argument to getFileInfo() to disable adding the size of
mountpoints to a directory's size.

Backport of 614e4d485c8b74f6879c401f8cbb93e9335bf9b3
Fixed quota calculation to also exclude ext storage
Fixed ext storage free space to not be restricted by quota
Fixed storage stats to be based on current directory

Previously, the storage statistics were always for the root dir.
This means that the upload button would always show the limit for the
root dir, even when uploading to a shared dir or external storage.

This fix adds a "dir" argument to getstoragestats.php.

Partial backport of 31181e4348b9af2625cf4d6ad38cf4cd81db3c1f
Merge pull request #5934 from owncloud/stable5-excludeextstoragefromquota

[Stable5] Exclude ext storage from quota