[ENH ]Tool box filter

[ales-erjavec]

Issue

Closes https://github.com/biolab/orange3/issues/6447

Changes

Implement filter/search for the widget toolbox.

[codecov-commenter]

Codecov Report

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

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

Additional details and impacted files

```diff @@ 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](https://app.codecov.io/gh/biolab/orange-canvas-core/pull/276?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=biolab) | Coverage Δ | | |---|---|---| | [orangecanvas/application/canvasmain.py](https://app.codecov.io/gh/biolab/orange-canvas-core/pull/276?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=biolab#diff-b3JhbmdlY2FudmFzL2FwcGxpY2F0aW9uL2NhbnZhc21haW4ucHk=) | `69.67% <ø> (ø)` | | | [orangecanvas/registry/utils.py](https://app.codecov.io/gh/biolab/orange-canvas-core/pull/276?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=biolab#diff-b3JhbmdlY2FudmFzL3JlZ2lzdHJ5L3V0aWxzLnB5) | `90.27% <66.66%> (-3.38%)` | :arrow_down: | | [orangecanvas/application/widgettoolbox.py](https://app.codecov.io/gh/biolab/orange-canvas-core/pull/276?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=biolab#diff-b3JhbmdlY2FudmFzL2FwcGxpY2F0aW9uL3dpZGdldHRvb2xib3gucHk=) | `73.92% <89.33%> (+12.63%)` | :arrow_up: | | [orangecanvas/gui/toolgrid.py](https://app.codecov.io/gh/biolab/orange-canvas-core/pull/276?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=biolab#diff-b3JhbmdlY2FudmFzL2d1aS90b29sZ3JpZC5weQ==) | `82.13% <96.87%> (+1.38%)` | :arrow_up: | | [orangecanvas/document/quickmenu.py](https://app.codecov.io/gh/biolab/orange-canvas-core/pull/276?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=biolab#diff-b3JhbmdlY2FudmFzL2RvY3VtZW50L3F1aWNrbWVudS5weQ==) | `68.88% <100.00%> (+0.11%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/biolab/orange-canvas-core/pull/276/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=biolab)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[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.