Further realtime improvements

A number of new features / enhancements;

* Display IF/TSS or Elevation/Grade in the controller
  when a workout is selected.

* Added buttons for forward/back which emulate the
  forward/back from a computrainer controller

* Added a slider to increase and decrease intensity/grade
  on-the-fly (during a workout), tied in with the
  computrainer controller's + and - keys.

* Unpicked the manualOverride code previously implemented

Mostly, or at least for this release, fixes #494.

src/MainWindow.cpp

@@ -99,7 +99,7 @@ QList<MainWindow *> mainwindows; // keep track of all the MainWindows we have op
 MainWindow::MainWindow(const QDir &home) :
     home(home), session(0), isclean(false),
     zones_(new Zones), hrzones_(new HrZones),
-    ride(NULL)
+    ride(NULL), workout(NULL)
 {
 
     mainwindows.append(this); // add us to the list of open windows