Migrate callers to new MWFileProps::getPropsFromPath() method

Migrate callers to new MWFileProps::getPropsFromPath() method

* FSFile should not be responsible for handling this much logic.
* Make more MediaHandler classes aware of the fact that an object
  other than File might be passed in. Use the FSFile instead of a
  useless empty stdClass object.
* Also added more fields to FSFile::placeholderProps to make it
  more complete.

Change-Id: I9fe764b2a7261af507c6555e6a57273cf7d00d36