Issues [#1931020] and [#1935820]: Allow custom fields for summary. Fix repeating events causing duplicates. Add @file to DateIcalFeedsParser.inc

Applied patch #11 from [#1922658] to get around iCalcreator limitation with stream wrappers. Also made the amount of whitespace on blank lines consistent throughout the project.

- 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.