CI maintenance

[martukas]

Description

Routine maintenance of continuous integration pipelines:

• updated CircleCI scripts to ensure apt install steps are non-interactive
• bumped dead link checker version
• recreated controller UML diagram as rendered via separate dot file instead of embedded in Markdown: the online rendering service is no longer available.
• removed exec permissions for some files that don't need it

[codecov]

Codecov Report

Merging #1342 (f4c04b4) into master (bcfbfa8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1342   +/-   ##
=======================================
  Coverage   57.53%   57.53%           
=======================================
  Files         102      102           
  Lines        3471     3471           
  Branches      321      333   +12     
=======================================
  Hits         1997     1997           
  Misses       1474     1474           

Flag	Coverage Δ
common	95.90% <ø> (ø)
controller	57.37% <ø> (ø)
gui	29.42% <ø> (ø)

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