fix faceting in tm_g_km

[chlebowa]

Closes #665.

Added expression that drops unused levels of faceting variable before plotting, so that empty panels are not plotted.

[chlebowa]

I believe dropping unused levels is sufficient here as it results in no empty subplots taking up space.

In a reasonable majority of cases the faceting variable will have few values. In the minority of cases with many values, I believe the recommended solution is to manually change the plot size using the widgets in plot_with_settings ("expand" icon in top right corner).

[github-actions]

Unit Tests Summary

    1 files    33 suites   3s ⏱️
149 tests 149 ✔️ 0 💤 0 ❌
168 runs  168 ✔️ 0 💤 0 ❌

Results for commit 244d899.

♻️ This comment has been updated with latest results.

[mhallal1]

I have added some changes:

1. Pushed the dropping of the empty levels one level up
2. removed the condition for empty plot

[mhallal1]

I do agree with @chlebowa that the user shall manually update the height of the plots as he/she desires and it is not the responsibility of the module.

[mhallal1]

This solution prints the plots over each other instead of plotting in a grid when using show R code:

[chlebowa]

This solution prints the plots over each other instead of plotting in a grid when using show R code:

But not in the app 🤔

[chlebowa]

Introduced counting function again. Seems to work well now.

[mhallal1]

LGTM.