Update all bootswatch themes

All bootswatch themes are now kind of on par with the mkdocs theme, added

- fontawesome icons (arrow icons on next/previous buttons now show up)
- support for github/bitbucket links
- support for `theme_center_lead` switch

by copying over the relative parts of the mkdocs theme. The only part I could see that still does not work in these themes is the sizing of images.

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.

This closes #33.