Support remove changes in vocabulary activity diagram

[ledsoft]

As a user, I want to see term deletions in the vocabulary activity diagram (see below).

The diagram currently shows persists as bars going up and updates as bars going down. Added delete changes would thus be complicated. However, the change types are also differentiated by colors. Therefore, I propose to have the diagram as a regular barchart with all bars going up and using just colors to differentiate the change types.