Merge the Google Fonts and Google Fonts UI modules

Hi Baris,

With the admin interface tweaks patch I suggested (refer to #1068050: Admin settings interface tweaks) it might be a good idea to merge the Google Fonts and Google Fonts UI module into one module. The fields to enter the CSS selectors can now easily be integrated with the Font selection interface by showing them with the enabled fonts.

A developer can still choose not to use the CSS selector functionality by not filling in the fields and it saves you a tab on the admin interface.

Just a suggestion!... :)