Issue #1305938 by kristiaanvandeneynde and KarenS, Make sure the overlapping items work correctly with half hour grouping, and don't allow it for custom time groupings.

Follow up to #1323280, we should only omit minutes from the heading if the grouping has no minutes in it.

Issue #1268780 by drewkeller,  in calendar_preprocess_date_views_pager() seems to be incorrect when base_path() is /

Issue #1265616, Rework the calendar display links into tabs and the Add link into an action item, and add hook_calendar_links_alter().

Issue #1223500 Fix the day link in the year view to point to the day view rather than the year view.

Change the default setting for the day view and make sure that the style does not try to create overlap items if it is missing the groupby value (which the default view was doing.)

Issue #1222736 Fix export errors caused when previous export fix of using export plugins got broken by changes in Views.

Fix some granularity handling, note that all calendar row plugins must provide a date_id value, and start updates to README.txt.

Add a template for the item view, split the row processing out into the basic processing and a separate function for exploding a single item into the multiple values that may be needed in a calendar.

More tweaks to the calendar display links, we can't use pager links for those or the base argument is structured incorrectly for our pager's attempt to swap new values in. Also found some more references to  that needed to be switched to ->curday.

Add some validation to the style plugin. Prevent the invalid combination of overlapping items and missing groupby times. That creates an endless fatal loop.