[FEATURE] Heatmap analysis of habits (similar to GitHub contributions)

[tgarul]

Hello, big fan of the app, been using this for a few months now.

I would like to analyse my progress on a particular habit using heatmaps. This is the functionality I would like:

1. Checking (ticking) a habit produces a light green (or any other coloured) cell
2. Skipping a habit maintains the same colour of cell
3. Crossing a habit (x) causes the habit to produce a blank (unfilled) cell
4. Maintaining a streak gradually darkens the colour reaching a peak around 10 days

Many other apps (Habitkit, Checker) have a similar system for visualising the progress.

This view would be a second view that you can toggle-to or default-to in settings.

[Optional] A master heatmap that visualises progress across all your habits.