Simplified schema and tweaked some bits

Removed obsolete ContextAmplifiers and SpecialGraphic attributes
Improved documentation and svg READMEs
Changed air corridor symbols to lines
Updated affected csv files
Changed the location of the geometry exception tags
Changed the descriptions on the gct tags
We could continue going back and forth debating it here but it's probably not worth the time to do that.  Suffice it to say I moved it the way I thought it should be moved and you thought it should be moved the other way.  I have no problem changing it.