made the save as a bit more bullet proof..
As we had problems that files could not be saved that way...

Then we have a general schema with extensions as a key {ext}.
This way it can happen that the app gets an mp4 instead of a maya scene file out of the library.
The extension setting would prevent that.
And if it is empty it wont filter anything
Merge branch 'master' of git://github.com/nebukadhezer/tk-multi-workfiles into nebukadhezer-master
Merge branch 'master' into nebukadhezer-master
Tidied up addition of filtering by extension code and backed out change
to save_as when creating folders