replaces the floating groups/text I did in foo canvas dirs

fix issue with cropping and initial scroll region
utilise flags in update cycle for reposition and crop
reinstate some of old container functions

sub classing foo canvas...

contain  base  FooCanvasItems  to  draw features,  both  compound  and
non-compound.

CanvasItem is the first subclass, with an interface, which the rest of
the set inherit from.

Status:
Currently work in progress,  with some missing functionality in Glyph,
Text and Sequence Features