adding to shiny + making pairwise_group_heatmap diverging + making sig_stars have user defined color

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (5279b9d) 95.11% compared to head (426c82d) 95.11%.

:exclamation: Current head 426c82d differs from pull request most recent head af0b569. Consider uploading reports for the commit af0b569 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #76 +/- ## ======================================= Coverage 95.11% 95.11% ======================================= Files 32 32 Lines 880 880 ======================================= Hits 837 837 Misses 43 43 ``` | [Impacted Files](https://codecov.io/gh/nateosher/DM-ME/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [R/plot\_pairwise\_group\_heatmap.R](https://codecov.io/gh/nateosher/DM-ME/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Ui9wbG90X3BhaXJ3aXNlX2dyb3VwX2hlYXRtYXAuUg==) | `100.00% <100.00%> (ø)` | | | [R/sig\_stars.R](https://codecov.io/gh/nateosher/DM-ME/pull/76?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Ui9zaWdfc3RhcnMuUg==) | `100.00% <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=None). 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=None)

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