Extend FullCalendar implementation

[agileware-david]

This PR includes the following additions

• A tooltip that will display basic event information when hovering over an event label
• AJAX endpoint to load active CiviCRM events
• A 'sort by' filter to only display events of a certain type
• Added WP filter so wp-civi-ux users can customize the appearance of the event page
• Extra shortcode parameters to do the following without editing event-fullcalendar.js
  • Specify colours for the labels of different event types
  • Limit the scope of event types to be displayed
  • Specify a start date
  • Thumbnail images