Enable Ctrl+Click and Alt+Left navigation on local variables

Since ZeroBraneStudio supports jumping to the definition of a local variable, adding Ctrl/Cmd + Click navigation to jump to the definition (similar to other IDEs like Eclipse and NetBeans) was relatively easy. This change also add a simple "jump stack", which allows you to return back to the original position where you jumped from using Alt + Left.

An animation of how this works is shown here:

<img src="http://i.imgur.com/oL4algS.gif/>