Add customised Cosmo CSS
Add customised Cosmo CSS

To reproduce:

1. Change base font size to 20px.
2. Change pagination-color: rgb(50, 50, 50).
3. Change pagination-hover-color: rgb(0, 0, 0).
4. Switch Source Sans Pro for Open Sans (in the font import and
   the font family selections).

StevenMaude/pelican-bootstrap3-sm,StevenMaude/pelican-bootstrap3-sm