Implement whiteboard sync & save (#32)

* add whiteboard sync and add fabric.js for saving whiteboard

* save canvas to database

* fix code

* fix code

* compress canvas json data

* fix import

* update whiteboard gateway

* change whiteboard sync implementation

* remove obsolete imports

* small fixes

* Change blob to longblob

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Co-authored-by: Florian Raith <florianraith00@gmail.com>
Co-authored-by: Florian Raith <37345813+FlorianRaith@users.noreply.github.com>