Update quota value in client after scan and upload

After uploading, the quota value wasn't refreshed.
This fix refreshes the quota value after files have been scanned or
uploaded.
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.
Merge pull request #5711 from owncloud/quota-refreshquotainclientafteroperations

Fixes for "max upload size" value showed in the UI