imposition widgets on the right side of the window

that will contain spelling & speaker labeling stuff.

speaker labels are now referred to as 'slabels' in the code,
 to avoid confusion with gtklabels.
a few extra labels  in the sidebar

and an ugly attempt at overriding the window's .background thing.
backgrounds & borders need to be figured out.
making .miscolorized class work by applying

the same style to the descendent label.
fixing Math::Roundeth::nearest to apparently

overcome some floating point error for now.
spell checker dummy widget into a dummu module.
separating transcript model & textview stuff into

a new module, Wordbath::TextView.
moving speaker labeling stuff to Wb::Transcript.