Adding open graph data

Adding new setting options for adding a custom **favicon**, specifying **open graph data** values for sharing site on social media, and adding some new settings in the General category for *site name* and *site url*. Newly added settings have been wrapped up into the Setting caching approach, so the queries are not repeated if not necessary.

Also starts process of trying to clean up the *General Settings* to separate them into more logical setting groups instead of one long page of settings all over the place.

Resolves #405, #192

@angaither 

CC: @barryclark @DFurnes