worker.tasks: update FlightPathChunks inside async task only

This saves a couple of 100 ms per flight on upload in the frontend.
lib.geo: add FEET_PER_METER constant

[18:56:58] <roeles> please, do not repeat magic constants :)
fabfile: adjust for new server environment
mapproxy.yaml: use maps.skylines.aero as wms URL

And don't check the certificate, otherwise mapproxy would fail.
app.py: check if g object has current_user

<_Turbo_> and added "hasattr(g, 'current_user') and" to the error
handling filter in app.py to be able to even get that error mail
setup.py: update werkzeug to 0.9.6
commands.import.airspace: adopt xcsoar's airspace class parsing

This will make it easier to use xcsoar's airspace intrusion code.
model.airspace: use xcsoar for airspace infringement detection

In general this is twice as fast as the postgis approach, speeding
up to 5 times for flights through many airspaces.

As a side effect, xcsoar already knows how to handle flight levels
or altitudes above ground.
model.airspace: return uppercase airspace references

And fix the SI units in get_airspace_infringements
model.airspace: replace NOTAM and UNKNOWN airspace references

XCSoar doesn't know them. Replace with MSL for now...
mapserver: update airspaces
airspace.map: update airspace class names
model.airspace: check configured airspaces only
model.airspace: use QNH if available