Initial release

There are two source plugins. One that is usable with all entities in core, except for terms. The second source plugin for terms extends the first and add some extra data for the sake of exporting term hierarchy.

Development version.

First beta relese.

Adding a new field of AddtoCalendar type

Below settings are only available in Add to calendar field:-

* Disabled Text: Text to be displayed if disabled.

* Start Date: Collect event start date and provide configuration similar to end
date.

* Show add to calendar widget: Available to end user for allowing the user to
disable the widget on particular event or expired events or show a message
like event expired from Disabled Text option.

Fix all issues