This makes the fullscreen editor much more powerful in terms of navigating
through chapters and scenes. This should make issue #234 users happy and
fix#444.
Top panel now has left/right arrows to navigate through the scenes. It will
automatically find the next/previous text item and display it, navigating through
the outline tree.
There's also a "New document" icon which will create a new text entry immediately
after the current one and switch to it.
Navigation can also be done using Alt+Page-Up, Alt+Page-Down or Alt+Left and Alt+right
shortcuts (Fixing #444).
There's now also the option between Title or Path for the top panel, if Path is chosen
then the full path of the scene is displayed and clicking on the scene or parent items
opens a menu to quickly switch to the selected chapter/scene. Selecting a folder will
automatically display the first text entry available in that folder.
