Change Patreon link to use slug. Resolve #7.
Change Patreon link to use slug. Resolve #7.

Since the social icons links use slugs instead of the full link,
I thought I should change the Patreon banner to do the same.
Also, people can now specify any image to use as the Patreon banner
so it can be made visible on light themes.

Shadow53/BluestNight,Shadow53/BluestNight,Shadow53/BluestNight