[ENH ]Tool box filter

[ales-erjavec]

Issue

Closes biolab/orange3#6447

Changes

Implement filter/search for the widget toolbox.

[codecov-commenter]

Codecov Report

Patch coverage: 89.83% and project coverage change: +0.18 🎉

Comparison is base (1c90038) 75.30% compared to head (77bd229) 75.49%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #276      +/-   ##
==========================================
+ Coverage   75.30%   75.49%   +0.18%     
==========================================
  Files          99       99              
  Lines       20953    21032      +79     
==========================================
+ Hits        15779    15878      +99     
+ Misses       5174     5154      -20     

Impacted Files	Coverage Δ
orangecanvas/application/canvasmain.py	69.67% <ø> (ø)
orangecanvas/registry/utils.py	90.27% <66.66%> (-3.38%)	⬇️
orangecanvas/application/widgettoolbox.py	73.92% <89.33%> (+12.63%)	⬆️
orangecanvas/gui/toolgrid.py	82.13% <96.87%> (+1.38%)	⬆️
orangecanvas/document/quickmenu.py	68.88% <100.00%> (+0.11%)	⬆️

... and 1 file with indirect coverage changes

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[janezd]

This is probably unrelated, but you may fix it as a part of this issue if you will.

Tabs are set not to be exclusive. Titles are colored. I open one tab, e.g. Model, close it and move the mouse out. Its color changes to gray.