Add dbus hightlight hint

[fwsmit]

Fixes #861

[codecov-commenter]

Codecov Report

Merging #862 (933f150) into master (b77f76f) will increase coverage by 0.00%.
The diff coverage is 62.50%.

@@           Coverage Diff           @@
##           master     #862   +/-   ##
=======================================
  Coverage   58.08%   58.09%           
=======================================
  Files          37       37           
  Lines        6101     6109    +8     
=======================================
+ Hits         3544     3549    +5     
- Misses       2557     2560    +3     

Flag	Coverage Δ
unittests	58.09% <62.50%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
src/dbus.c	63.12% <62.50%> (-0.02%)	⬇️

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[fwsmit]

@tsipinakis I've fixed the merge conflict for this PR.

There's still the questionable behaviour of setting the attributes before the rules are evaluated. This is problematic, because in settings refactor V2 everything is made a rule, even the [urgency_*] sections. This means that the dbus hints would not do anything, because they were overwritten by the rules. This should be fixed in c463a59