Add github_fork option to the main theme
Use github_fork option in the main theme layout
Make the index_logo option default to not-true.

This solves the problem described in https://github.com/mitsuhiko/flask-sphinx-themes/commit/0269f3d188eaff07c44a800f35f7351f9e0aefb0#commitcomment-4916032
theme.conf: Added github_ribbon_color option
Merge remote-tracking branch 'joar/patch-1'
Merge branch 'github-ribbon'

Conflicts:
	flask/theme.conf