Changed the FileSubsites->canEdit method

It will now return true if the current user owns the file which would be very useful if you are allowing users to edit the file through and frontend form. The canEdit method will also check and return true if the current logged in user user has CMS_ACCESS_AssetAdmin or CMS_ACCESS_LeftAndMain permissions set
If canEdit is called with a $member value then we shouldn't assume we are checking against the current user. You'll need to take this into consideration here.

E.g. we may need to check `$file->canEdit($someOtherUser)` to see if that user can edit the file, even if they aren't logged in.