Refactor MainWindow Part 2 of 5

Decoupled classes from MainWindow to reference Context
and Athlete (and introduced a couple of new headers).

We no longer pass around a MainWindow pointer to children
but pass a context instead.

There are still a few pieces left in MainWindow that need
to move to a better place;
    * Setting/clearing filter selection
    * Working with Intervals
    * Adding/Deleting Rides
    * Save on Exit

As mentioned previously there are lots of other parts to
this refactor left to do;
    * 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

src/MetadataWindow.cpp

@@ -18,8 +18,8 @@
 
 #include "MetadataWindow.h"
 
-MetadataWindow::MetadataWindow(MainWindow *mainWindow) :
-    GcChartWindow(mainWindow), mainWindow(mainWindow)
+MetadataWindow::MetadataWindow(Context *context) :
+    GcChartWindow(context), context(context)
 {
     setInstanceName("Metadata Window");
     setControls(NULL);
@@ -28,7 +28,7 @@ MetadataWindow::MetadataWindow(MainWindow *mainWindow) :
 
     QVBoxLayout *vlayout = new QVBoxLayout;
     vlayout->setSpacing(0);
-    rideMetadata = new RideMetadata(mainWindow);
+    rideMetadata = new RideMetadata(context);
     QFont font;
     font.setPointSize(font.pointSize());
     rideMetadata->setFont(font);