Fix #12, sidebar icons for file-types fully implemented

As the title implies, the issue #12 will be fixed with this pull-request of doom.

+ Most of it is just a bunch of icons, generated files, etc.
+ Actual code changes is minimal.
+ Illustrator files where original work is done is provided as much as possible.

**README.md** should be updated to reflect the changes, but I don't know how @lefoy wants to word this...