MainWindow Refactor Part 1 of 5

Breaking the MainWindow 'god object' into
separate classes for Athlete and Context.

Further updates will need to;
- break MainWindow Gui elements into Toolbar and Views

- migrate from RideItem and Ridelist to ActivityCollection
  and Activity classes that are not tied into gui elements.

- introduce Application Context and AthleteCollection

Once these are done we will be in a position to decouple
most classes from mainwindow and also introduce tabbed
athletes.