Add legend

[pietervdvn]

Add a frame which shows where each route goes to, what colour it has and (if applicable) what the routenumber is

[xivk]

We need something like there was in the previous version of the brussels routeplanner:

[xivk]

Add another button on top next to the hamburger menu to show/hide this but show it by default when the routeplanner is loaded.

[pietervdvn]

I've added an initial legend, visible in the genk tab iff no route is loaded. They are clickable, although no action is taken if they are clicked yet.