Fix rotation and flipping for parts, closes #68, introduce new draw mechanics for part, closes #66
Force text to stay horizontal
Minor refactor, add coords_average function
Fix rotation direction after flipping
Fix wire rotation, single and grouped
Fix offset regression of group rotation for parts
Grid refactor

Split grid into model and view (grid and grid_item), probably useful for future stuff like embedding schematics into schematics, also cleaner from a design point of view. Add a pointer to grid (model) item-data in order easily retrieve the align target.
Properly hook grid into model items, partial implementation

Loading items does not associate them with the sheet grid!
This will lead to misplacment after rotation or flipping - for now.
Add item_data_snap, remove dead code chunks
Remove overlapping signal "changed" of wire and item-data
Properly unregister items on removal

Due to a missing unregister call, connection dots would remain.
Also fixes a bunch of warnings and whitespaces errors
Fix wire snapping on rotation and drag and drop
Fix whitespace errors
Rebase Grid away from ItemData ontop of GObject, add biased snapping
Add UNUSED macro
Minor README changes
Grid hooks, minor internal grid fixes and property handling

Also many many whitespace errors
Merge pull request #70 from drahnr/new-view-mechanics

Manual intervention was required
Add kbd tags, add color highlighting to snippets
Add reference to mailinglist, closes #20