The choose cyclist dialog allows you to open
a cyclist that is already open. This is not
a great idea since the two windows will conflict.
This patch introduces a global vraiable to track
open windows (mainwindows) and MainWindow maintains
it as it opens and closes.
AthleteTool still needs to be updated to refresh
as new cyclists are created (and when its written
deleted).
Since a large number of user 'bug' reports and
worse, coding errors, are caused by mishandling
user setup (missing CP, HR parameters, Zones, Weight)
the new cyclist dialog now prompts the user for basic
parameters when creating a new cyclist.