Improvements!

- Fixed imports
- Added the type and date metadata for walls.
- Added date parsing. Using the date in the URL for now.
- Added the use_info optional param to download_walls. When this is set
to true, it will use "{date} {name} {resolution}.jpg" for the filename
instead of the original filename.
- Added the type filter to download_walls, so that you can restrict the
downloading to only release walls or only media walls (as the media
walls don't generally change).

Still need to do that argparse front end...
Merge remote-tracking branch 'origin/master'

Conflicts:
	GW2Walls.py