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
It appears that these "gct_"'s got moved the wrong way - they should appear **in front of** the 2525c id 

not:
G*GPPF----****X;MAIN;**gct_arrow;**
but:
**gct_arrow;**;G*GPPF----****X;MAIN;`

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