Add single airspace edit modal to airspace viewer tool

[reskume]

Currently the airspace viewer won't show invalid airspaces. To fix self-intersections, it would be useful to have another tool that allows a single airspace OpenAIR definition input and shows the possibly invalid airspace on the map. This allows to fix airspaces in-place instead of opening up another "Create new airspace" page and use the openair input there to fix the invalid geometry.