Removed everything associated with image download

In an effort to comply with the Unix philosophy - this tool should do
one thing (get wallbase.cc image URLs) and do it well. Other tools can
be combined with this one to download the images.
Updated the app description

Also updated all copyright notices to exclude the app description for
easier future description changes
Added option to show progress
Fixed tests
Added first version of the man page
Updated man page
Fixed arg parsing test
Updated README.md