Remaining space and upload error notifications fixes

This fixes several issues with remaining space and notifications:
* Upload errors for single file uploads were not being shown properly
* Max upload size was only refreshed every 5 min, so if you opened the page with a 100% quota even after deleting files you needed to wait for 5 min before you could upload new one.
* Upload errors were not using OC.Notification
* Percentage used was not being returned on uploads so quota warnings could not be shown

OC.Notifications still needs a full revamp as it is almost useless as it is now.