.. now can drag and drop any date range onto the
home view compare pane to compatre different
seasons, and even across athletes.
.. we setup the metrics and measures in the context
so the charts don't have to, but we still need to
reference the source context for bests and ridefilecache
data
NOTE: We need a mechanism for 'locking' source tabs/athletes
when they are part of a compare to avoid crashing when
a context is deleted whilst we are comparing
NOTE: We till need a way to remove entries from the compare
pane, possibly call it when an athlete is closed too
(see note above).