Rainlendar 2.8 Beta 98

# Changes:
- Changed the calendar selection to combo box. The "Allow multiple calendars" in advanced settings can be used to go back to the old way.
- Added "w" and "h" attributes for the days element in the calendar which can be used to define the size of the day in the free layout.
- Rainlendar_SetVariable() didn't work. Fixed.
- Added a special calendar called "[None]" to the included/excluded calendar list which can be used to show/hide events which do not belong to any calendar.
- If the window fade duration is set to 0 the window is set immediately to opaque. This should help with the hidden windows on Linux.
- Added an advanced option to show/hide the tooltip in the tray.
- It's now possible to add a time offset for a calendar's events and tasks. This can be used e.g. for time zone adjustment.