Update all bootswatch themes

All bootswatch themes are now kind of on par with the mkdocs theme, added

- fontawesome icons
- support for github/bitbucket links
- support for `theme_center_lead` switch

by copying over the relative parts of the mkdocs theme. The image sizes are still only good in the mkdocs theme though.

Since they're all pretty much identical except for the readthedocs theme it would be good idea to have some sort of master-theme to put all this in, the diff is **gigantic** but it is all just copy paste to bump up the other themes.