Update sql queries and extend mutation color palette

[johausmann]

• Updated raw SQL queries in queries.py to use SQLAlchemy text clause object and parameter substitution via placeholders.
• Enhanced color palette for mutation statistics plots (inherited from ColorBrewer palette used previously).

[codecov[bot]]

Codecov Report

Base: 83.21% // Head: 83.21% // No change to project coverage :thumbsup:

Coverage data is based on head (ac46a7d) compared to base (5185585). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #87 +/- ## ======================================== Coverage 83.21% 83.21% ======================================== Files 46 46 Lines 4218 4218 ======================================== Hits 3510 3510 Misses 708 708 ``` | [Impacted Files](https://codecov.io/gh/TRON-Bioinformatics/covigator/pull/87?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TRON-Bioinformatics) | Coverage Δ | | |---|---|---| | [covigator/dashboard/figures/\_\_init\_\_.py](https://codecov.io/gh/TRON-Bioinformatics/covigator/pull/87?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TRON-Bioinformatics#diff-Y292aWdhdG9yL2Rhc2hib2FyZC9maWd1cmVzL19faW5pdF9fLnB5) | `100.00% <ø> (ø)` | | | [covigator/dashboard/figures/mutation\_stats.py](https://codecov.io/gh/TRON-Bioinformatics/covigator/pull/87?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TRON-Bioinformatics#diff-Y292aWdhdG9yL2Rhc2hib2FyZC9maWd1cmVzL211dGF0aW9uX3N0YXRzLnB5) | `70.96% <ø> (ø)` | | | [covigator/database/queries.py](https://codecov.io/gh/TRON-Bioinformatics/covigator/pull/87?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TRON-Bioinformatics#diff-Y292aWdhdG9yL2RhdGFiYXNlL3F1ZXJpZXMucHk=) | `70.12% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TRON-Bioinformatics). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TRON-Bioinformatics)

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