GraphicLayerSwitcher: new graphical layer switcher, first iteration

This one will be extended to support selection of arbitary map overlays.
And it works in mobile browsers :-)
Remove unused SimpleLayerSwitcher files
GraphicLayerSwitcher: don't show current layer's name
GraphicLayerSwitcher: show layer selector on click only
GraphicLayerSwitcher: highlight current selection / image on mouseover
GraphicLayerSwitcher: better image for shaded relief layer
GraphicLayerSwitcher: move creation of current icon out of loop
GraphicLayerSwitcher: prepare adding a second layer box (overlay layers)
GraphicLayerSwitcher: show layer selector for overlays
map.js: remove airspace baselayer
map.js: add empty layer
Add missing layer preview images
GraphicLayerSwitcher: grey out unused overlay layers
GraphicalLayerSwitcher: reorganise code
GraphicLayerSwitcher: don't redraw layer switcher on visibility change of baseLayer
GraphicLayerSwitcher: don't close layer switcher on baseLayer change
map.js: only hide airspace layer if desired
templates/users/view: rename takeoff locations layer, add layer image
airspace.map: reduce outline width

Makes the map look cleaner
assets/airspace: update airspaces