[FIX] widget: Make controlAreaVisible a global setting

[ales-erjavec]

Issue

Make controlAreaVisible a global setting along the widget geometry.

Description of changes

Make controlAreaVisible a global setting

Includes

• Code changes
• Tests
• Documentation

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.03%. Comparing base (c28fde3) to head (13e174b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #282   +/-   ##
=======================================
  Coverage   72.03%   72.03%           
=======================================
  Files          34       34           
  Lines        9117     9117           
=======================================
  Hits         6567     6567           
  Misses       2550     2550           

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[markotoplak]

@ales-erjavec, thanks, this change means that now a newly added widget could be shown with a hidden control area. @janezd (and me) pointed out that for new widgets, the control area should always be shown. The size is problematic: if a default was saved with a hidden control area, the new widget size should be increased in width by the control area size.