Changed parsers/saves to parsers/files

This better reflects its purpose (eg, it can also parse .mod files)
Removed extraneous imports
Added mod support.

Can support standard mods (issue #5), and workshop mods (issue #6).

Currently will only auto-detect mod directory on windows.

Currently does not clean up after itself wrt extracted files (which is
only provinces.bmp).  Shouldn't be a major issue; it's in a temp folder,
after all, and it isn't sensitive information.
Loading of map and country data is now deferred.

This is necessary because, if a compressed mod is loaded, this can take
a relatively long time, which might give the impression that the app had
hung.
Moved saving functionality to viewer from map.

This enables the image to be annotated.
Updated readme with mod information.