Add tooltip warning about long scenario names in db editor

[PiispaH]

Increased the amount of scenario names' characters in generated subdirectories from 15 to 20.

Re spine-tools/Spine-Toolbox#2081

Checklist before merging

• [x] Documentation (also in Toolbox repo) is up-to-date
• [x] Release notes in Toolbox repo have been updated
• [x] Unit tests have been added/updated accordingly
• [x] Code has been formatted by black
• [x] Unit tests pass

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (5198ecd) 55.07% compared to head (cf1b9ca) 55.07%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #142 +/- ## ======================================= Coverage 55.07% 55.07% ======================================= Files 192 192 Lines 17362 17362 Branches 2846 2846 ======================================= Hits 9562 9562 Misses 7307 7307 Partials 493 493 ``` | [Impacted Files](https://app.codecov.io/gh/spine-tools/spine-items/pull/142?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spine-tools) | Coverage Δ | | |---|---|---| | [spine\_items/utils.py](https://app.codecov.io/gh/spine-tools/spine-items/pull/142?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spine-tools#diff-c3BpbmVfaXRlbXMvdXRpbHMucHk=) | `63.91% <0.00%> (ø)` | |

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