Merge pull request #20 from TobiasLohner/airspace_info

Airspace info
model/tracking: Accept numeric values in delay_filter()
model/tracking: Added documentation to delay_filter()
Add Mountain Wave Project layer
map-click-handler.js: split formatting and logic code
map-click-handler.js: prepare displaying more than airspace data only
map-click-handler.js: show mountain wave info
map.js: save visible layers by layer switcher, remember visible overlay layers