Increase Functionality

There is now a way to exit the program the doesn't require having two
monitors. After logging in there is an exit button in the toolbar. On
pressing said button a dialog will appear asking for an exit code. If
the correct code is entered, the program will close.

The tabs were also updated and the program will now load a pdf. Right
now it points to my desktop, but editing the path in mainwindow.cpp will
fix that. The muPDF-qt library will render the pdf to an image. There
doesn't seem to be a way to render it as anything else right now, but I
will be examining the muPDF standard library for an idea of how to fix
that.