* ordering provider ensures sequence flows appear
behind tasks
* importer makes sure we render elements in the order
lanes > sequence flows > other flow elements
* consistent minimal opacity ensures elements in
front of tasks don't look _connected_
Closes#727
The way we create labels during import (right after the respective
element) interfered with the ordering during boundary attach.
This commit fixes the behavior.
Closes#437
Nico Rehwaldt
Philipp Fromme
Vladimirs Katusenoks
pedesen