[FIX] Silhouette plot text width

[ales-erjavec]

Issue

Closes gh-5728

Description of changes

• Do not clip child text items in the text annotations list.
• Allow the text to be wider (but is still limited to 750px; was 300 before)
• Generally change how the tool tips are displayed in the GraphicsTextListWidget with associated changes to all its uses (int owheatmap and owdistancemap). Before tool tips were set on individual text items, now the widget responds to QGraphicsSceneHelpEvent).
• Allow any Discrete it String variable for text Annotations.
• Also fix misaligned top/bottom axes

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #5756 (6645e31) into master (300dbba) will decrease coverage by 0.04%.
The diff coverage is 64.63%.

@@            Coverage Diff             @@
##           master    #5756      +/-   ##
==========================================
- Coverage   86.15%   86.10%   -0.05%     
==========================================
  Files         315      316       +1     
  Lines       66186    66307     +121     
==========================================
+ Hits        57023    57095      +72     
- Misses       9163     9212      +49