Custom legenda

[MatisseBE]

As per the title

Context: The initial idea for an (optional) legend came from my frustration that ETCS L2 and ETCS L1 in a tunnel looks almost identical.
Being able to change the colors would go a long way for most of the layers, however this discussion made me realise there might be more to it, especially in the train protection system's layer.

• Optional
• Ability to turn off shades from tunnels
• Code like interface that is easy to understand
• Ability to save custom rules
• Ability to add custom tags (here: different train protection systems that are not listed)
• Ability to reorder the list easily

Veryyy rough mock-up for the signalling layer:

[MatisseBE]

Initially, it would already be a great improvement if we could change default colors of the predefined legend ourselves. Perhaps with the ability to turn off shades for tunnels.