Created formatmanager.py which will be used for managing all the various format modules contained in the formats folder. This works like the plugins manager by automatically loading all the format modules and converting them to Format objects.

The format manager has 3 attributes which can be used to access all the Format classes:
formats -- maps file extensions to their corresponding Format objects
imports -- a list of all format objects to be used in importing
exports -- a list of all Format objects to be used in exporting
Changed each format file to contain new format manager attributes (name, importexport, extensions, export_options) in order to be able to be used in new format managing system.
Fixed a bug made in 2114f27 where saving always resulted in calling Save As. Fixed to now only save .mg2 and .mg formats.