Refactor urgency notification logic

In preparation to future notification logic, the urgency hint should already get their own logic.

Related to ff4e91e4 and #57 (closed).

changed milestone to %GTK 0.1.0-beta1

added T: task label

enabled an automatic merge when the pipeline for 42329da9 succeeds

aborted the automatic merge because source branch was updated

added 1 commit

• 971977d7 - Refactor urgency notification logic

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merged