The update hook now also checks for importers which are set to the new parser,
but still have un-capitalized source keys. This will help users who forget to
run the database update before manually fixing the missing
DateIcalIcalcreatorParser warning.

This commit adds the migration code that converts all Feeds Importers which used
the DateIcalIcalcreatorParser plugin to use DateiCalFeedsImporter instead. The
old classes have been removed.

Also updated the README to reference the iCalcreator GitHub.

Date iCal now requires Views v3.5+.

- Issue #1529506, Added optional webcal:// support.
- Issue #1890736, Added ability to exclude the X-WR-CALNAME property.
- Issue #1565410, Sites with "Clean URLs" disabled can now download feeds normally.
- Several minor bigfixes, and cleanup of the iCal icon theming.

Includes patches from issues 1895396 and 1462646.
Updated the README and the CHANGELOG.