SciDAVis - Improvements SVN-temp

- fixed empty project explorer when starting for the first time

- fixed bug #1813115: scidavis crashes when opening column
or axic options menue
- fixed some Grid related issues

- removed AbstractAspect from the base classes of
AbstractSimpleFilter since I think an undo aware
class that manages the filter is better than implementing
undo commands for all filters
- improved AbstractSimpleFilter
- improved SimpleCopyThroughFilter
- wrote a SimpleMappingFilter and added a test case
for it to the column unit test

- did some renaming for consitancy and to avoid naming conflicts
- polished/improved AbstractFilter and AbstractSimpleFilter

- implemented conversion between SciDAVis enum values
and strings using the meta object system
- implemented save/load to/from XML for columns

- improved the way comments are displayed in table headers

- added/revised some more icons for table actions

- added some new icons for table actions

- added files I forgot in previous commit

- added icons for the 3 column types
- implemented column sorting
- implemented several more Table methods
- added support for dragging columns to another position in tables
- added support for undo stack macros to AbstractAspect
- added preliminary method to manage systemwide keyboard
shortcuts in Project