fix heatmap if cell type combination not symmetrical

[zktuong]

first figure out the base code to fix the pvalue side (focusing on the columns) before attempting #101

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (54b8a69) 73.18% compared to head (551ad19) 73.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #102 +/- ## ========================================== + Coverage 73.18% 73.96% +0.77% ========================================== Files 9 9 Lines 2055 2055 ========================================== + Hits 1504 1520 +16 + Misses 551 535 -16 ``` | [Files](https://app.codecov.io/gh/zktuong/ktplots/pull/102?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong) | Coverage Δ | | |---|---|---| | [R/plot\_cpdb\_heatmap.R](https://app.codecov.io/gh/zktuong/ktplots/pull/102?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong#diff-Ui9wbG90X2NwZGJfaGVhdG1hcC5S) | `98.46% <100.00%> (+24.61%)` | :arrow_up: | | [R/utils.R](https://app.codecov.io/gh/zktuong/ktplots/pull/102?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zewen+Kelvin+Tuong#diff-Ui91dGlscy5S) | `86.88% <100.00%> (ø)` | |