Add the ability to load special template files for the default themes.

* This commit includes templates for Twenty Fifteen.
* Also allows a theme-specific stylesheet to be enqueued.
Merge branch 'compat'
Add the `pagination` class to eventbrite_paging_nav() output.

Adds styling compatibility with the `the_pagination()` template tag introduced in WordPress 4.1.
Add body classes when Eventbrite templates are in use.
Rename Eventbrite_Rewrite class to Eventbrite_Templates.
Correct docblock description.
Add compat files for the Twenty Fourteen default theme.
Add a <span> to the default meta separator for CSS selecting.
Improve styling for event meta in Twenty Fifteen.
Add additional <span> markup to event meta for better Genericon handling in default themes.
Add compat files for the Twenty Thirteen default theme.
Add compat files for the Twenty Twelve default theme.
Improve body classes when on Eventbrite templates.
Correct stylesheet descriptions.
Add compat files for the Twenty Eleven default theme.