Rework layouting / all labels repositionable

* Work done as HEMERA-3136
* Fixes / improvements
** Connections have labels using the common label feature (HEMERA-3142)
** Labels are always displayed on top (HEMERA-3753)
** Activities have right size and position when being added to parent
containers (HEMERA-3757)
** Bendpoints correctly handeled during import (HEMERA-3750)
** Label import is tested now (HEMERA-3751)
** Implement connection and shape utilities (HEMERA-3730)
** Utilities are restructured

** Various other improvements (+50 test cases)
Merge changes from HEMERA-3136-sequenceflow-labels