Refactor sendKeyboard functions to new funcs, propogate constness

The sendKeyboardBackspace function was used with a non-const parameter
throughout the entire inheritance hierachy. Const has been added to
every parameter for the reasons you add const.

src/tabcontrollers/KeyboardInput.h

@@ -15,7 +15,7 @@ public:
 
     virtual void sendKeyboardInput( QString input ) = 0;
     virtual void sendKeyboardEnter() = 0;
-    virtual void sendKeyboardBackspace( int count ) = 0;
+    virtual void sendKeyboardBackspace( const int count ) = 0;
     virtual void sendKeyboardAltTab() = 0;
 };