interactive pane composition improved (-> ViConstraintLayout)

Vivide-mt.417
Code clean-up in constraint layout

Vivide-mt.418
preparing new-style script organization and interactive tool building with nested multi-pane widgets

Vivide-mt.419
- concept of #visibleNodes in widget api removed hand compeltely handled in panes/models

- workspaces can save again

- visible drop highlight for multi-pane widgets introduced

- some more code clean-up

Vivide-mt.420
pane connections refactored (Finally! :))

Vivide-mt.421
NEW: logging service to track user behavior

Vivide-mt.422
logging service works with CouchDB and basic auth; logging disabled by default, can be enabled and configured via preferences

Vivide-mt.423
screentshot logging can be deactivated if necessary

Vivide-mt.424
LOGGING: more script log points and frequent activity log added

Vivide-mt.425
FIX: watch for memory consumption in logger if network connection bad

MPW: multi-pane widget can generate meta-scripts for its contents

Vivide-mt.426
FIX: Vivide can be opened again

NEW: single pane editor (not used yet)

BETTER: some refactorings and code clean-up

Vivide-mt.427
Merge remote-tracking branch 'hpi/master'