Gitlab is a popular Git repository manager using an opensource license.
This commit adds the Gitlab social icon.

* Parmeterize number of recent posts in index.html

* Replace .Site.Params.recent_posts_number with $.Param "recent_posts_number" in index.html

* Adding support for favicon

* Fixing html tag

* add linkedin

* update github svg to fix spacing

* add colors from brandcolors.net

* add github social link

* add github css

* fix css error breaking rollover

* using Hero sample image in the theme's /static folder
* fall back to site config
* fall back to hard coded default if none set in page or site params

So it is runnable out-of-the-box.