Replace Google Maps with leaflet.js
Currently using opemstreetmap.org tiles as default but is able to
display Google Maps tiles via Googles API
Move #followAircraft to the left due to leaflet conflicts
Code cleanup
Fix resize on fullscreen
Remove weird sidebar button hover effects
Merge pull request #48 from denschub/leaflet

[Refactor] Use Leaflet
add Leaflet.EasyButton webjar
googleMapsApiLoaded is only used once
Replace the dedicated 'follow aircraft' button with a map control
Merge pull request #49 from denschub/follow-button

Use Leaflet control to follow the aircraft