Rainlendar 2.8 Beta 92

* Changes:

- The category filters are now case insensitive.
- Month view didn't show multiple events on the same day correctly. Fixed.
- Weekly recurring events did not take into account the interval when calculating the end date.
- Restoring a backup didn't apply the settings. Fixed.
- Added possibility to create custom categories for skins which support them.
- "Custom category icon path" in advanced options can be used to define a folder for custom icons.
- Added "Open containing folder" for the skin's context menu in the options dialog.
- Added %HF as header format code which will be replaced with the default header text.