Switchable Dark Theme - Attempt 2 - Ongoing

[Laimonade]

Hey! :) Here's my second attempt at implementing a theme switching for Bela's IDE.

The approach here is to use SCSS @mixin and a map, allowing to define a colour variables for each of the themes.

The main logic and colour variable definitions are located in IDE/frontend-dev/scss/base.scss.

The idea is that we (only) move every specific element properties affected by the theme switching into a theme switching function (themify), performing the colour switch only on the relevant properties.

In each scss file containing elements which need to change colour, the relevant properties for the element is being moved at the top of the file inside of the themify function.

While this may not the cleanest of look, it allows 2 things:

1. To only transpile into css the relevant properties, rather than having an entire duplicate of the code for each added theme.
2. It gives a good base to support further themes. We only need to define the colour palettes and the rest of the infrastructure is already there.

There's still a bit of work to get this polished, but sharing now if people wants to start testing/using it before.

ps: You can discard the commit history before Feb 14, 2024. They shouldn't be in the commit history but not sure how to safely rewrite the history.