Rename 'monospace' class to 'favorite-font'
Set and bind font-family if unset

Default for desktop is monospace and default for mobile
is sans-serif
Remove font definition from css file

The font for the .favorite-font class is now set programmatically
Merge pull request #384 from glowing-bear/default-font

Make sure that a favourite font is always set when using Glowing Bear.
Plugin visibility defaults to value of rootScope.visible

And plugin content is shown if it has to be visible
contentForMessage doesn't have to care about content visibility
Rename rootScope.visible -> rootScope.auto_display_embedded_content

More verbose but more descriptive