Util/StringUtil: Add StringStartsWithIgnoreCase function
Airspace/AirspaceParser: Relax parsing of TNP airspace files

Fixes trac issue #3272.
Merge remote-tracking branches 'hjr/v6.7.x' and 'apf/v6.7.x' into v6.7.x
Manual en flash: Added 6 illustrations, GNU FDL permission granted by originators.