add hard coded locus feature set name, needed because code must search for this in requested feature sets.

rationalise feature set data held on canvas group. Add frame to list col data. Add colours for frames. Add frame to lots of funcs.

Make some of the feature set/feature code into externally callable routines so they can be used for 3 frame display.

make sure destroy handler run for dna/protein items. Add feature frame routine. All set date now in one struct on canvas group. Tidy up destroy function and make it work !

Add function to get strand/frame for a feature set canvas group, code to do better col. highlights, add frame to all hash calls.

add new encapsulated long item stuff, add frame stuff for hashes, add calls to create sets/delete sets/columns.

add new longitem calls for caching items that may need to be clipped. Make the item destructor remove the item from longitem.