Further MainWindow updates, this time moving the code
for working with intervals to the AnalysisSidebar and the
associate menus.
Ultimately, the functions for working with Activities and
their Intervals will move from MainWindow and Sidebars to
the ActivityCollection classes.
This is a step as we strip out MainWindow to just GUI
aspects.
Moving the code intertwined into MainWindow for
the analysis view sidebar; activity list, intervals
and calendar into a new AnalysisSidebar class.
WARNING!
This is a work in progress checkpoint commit
as the sidebar menus and context menus have
not yet been migrated out -- this will be done
in the next commit or two.
