Improve map layer selection panel

[josephbirkner]

The map layer selection panel needs various UX improvements:

• When folding out, it should not cover the toggle button, so it can be closed again without moving the mouse.
• It should not be a dialog, instead it should just be a plain panel which grows in vertical size as the number of contained map layers increases.
• Currently, it is not possible to toggle a map layer or a whole map on or off. The panel should present a show/hide button in line with each map and nested map-layer.

We should also use this opportunity to move the map layer panel into its own angular component.

[MisterGC]

Additions:

• The headline takes too much space and unnecessarely stands out (users should already know when they open the panel)
• don't repeat the map id for each layer as maps and layers are already grouped
• change the focus icon (magnifier glass!?), if I wouldn't know i'd associate the current one with show/hide
• the show/hide could then be just that eye (and crossed out or closed for not showing)
• show the icons next to the text entry not as a "fat" icon, same for the zoom selector!?
• Change the Add a label: "Tile Level" or "Zoom Level" before the zoom level selector (only applicable when the ctrl. is in a separate line)
• Make the control less bulky

[MisterGC]

Mockup we agreed on