Add new spine toolbox and -engine logos

[PiispaH]

New logos for toolbox and engine added into toolboxes as well as dp apis documentation start pages and into the readme of spine toolbox and spine engine.

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 coverage has no change and project coverage change: +0.27 :tada:

Comparison is base (e225ff5) 75.14% compared to head (b0c1707) 75.42%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #252 +/- ## ========================================== + Coverage 75.14% 75.42% +0.27% ========================================== Files 71 76 +5 Lines 10865 10889 +24 Branches 2361 2374 +13 ========================================== + Hits 8165 8213 +48 + Misses 2243 2236 -7 + Partials 457 440 -17 ``` [see 15 files with indirect coverage changes](https://app.codecov.io/gh/spine-tools/Spine-Database-API/pull/252/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spine-tools)

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