Add messaging core prototype

* Port drag / dragger / snapping
* Lost actual model execution (e.g. performing model move)
* Work on snapping / snap lines unfinished
Snapping and snap lines work correctly now
One more bug fix
Disable text selection during drag
Add event based dragging and dropping
(Re-)introduce event distinction between conns and shapes
Cleanup and recolor snap grid
Split grid and element snabbing
Connections reworked
Refactor util
Add redo / undo + shape movements
Bendpoint basics
Snapping for bendpoints
feat(bendpoint): moving and reattachement
fix(format): adjust Util module requires to case sensitive filesystem

the Util module was defined with lower case in the features, but the file has
upper case, this causes problems on some OS
improve(undo): undo redo key binding are registered in the feature

this should be the default behaviour, this might be customizable in the future
refactor(commandstack): seperate commandstack from undo feature

the commandstack is an important internal feature which is independent
from the undo functionality itself (which just triggers stack operations)
this makes the undo feature also more configurable in the future
feat(connection point): drag and anchor reattach

Connection points can be moved
- if they represent bendpoints, bendpoint move is executed
- if they represent anchor points anchor reattachement is done

Known issues:
- we have to check for a reliable way to fire drag over/out events.
  currently drag over / out is to often firing
Merge branch 'commandstack' into messaging
Merge branch 'messaging' into commandstack