Fix few issues in diff reports

[tfiedor]

1. Fix issue with sizing,
2. Reword some stuff,
3. Optimize flame graphs.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 98.97%. Comparing base (074a222) to head (b43630c).

Files	Patch %	Lines
perun/view_diff/report/run.py	87.50%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #200 +/- ## ========================================== - Coverage 98.98% 98.97% -0.02% ========================================== Files 144 144 Lines 9857 9854 -3 ========================================== - Hits 9757 9753 -4 - Misses 100 101 +1 ``` | [Flag](https://app.codecov.io/gh/Perfexionists/perun/pull/200/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Perfexionists) | Coverage Δ | | |---|---|---| | [coverage-3.10](https://app.codecov.io/gh/Perfexionists/perun/pull/200/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Perfexionists) | `98.97% <87.50%> (-0.02%)` | :arrow_down: | | [coverage-3.11](https://app.codecov.io/gh/Perfexionists/perun/pull/200/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Perfexionists) | `98.96% <87.50%> (-0.02%)` | :arrow_down: | | [coverage-3.12](https://app.codecov.io/gh/Perfexionists/perun/pull/200/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Perfexionists) | `98.96% <87.50%> (-0.02%)` | :arrow_down: | | [coverage-3.9](https://app.codecov.io/gh/Perfexionists/perun/pull/200/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Perfexionists) | `98.96% <87.50%> (-0.02%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Perfexionists#carryforward-flags-in-the-pull-request-comment) to find out more.

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