Allow global annotation shading to be specified via alignment Annotation Files

Jalview annotation files in 2.11.5.x do not provide a way to configure the global shading scheme, whilst it does provide a way to specify colourshemes for groups defined on the alignment via a 'PROPERTIES' statement.

Rather than ask people to manually configure shading, or specify command line options, we could introduce a VIEW_PROPERTIES statement (or equiv) that allows configuration of global shading schemes such as 'Colour by annotation'.