Fixed client/server widgets not displaying

Now gets sizeHint from widgets instead of window.
Initialized pointers to nullptr

Doesn't change anything, but better safe than sorry.
Transitioning

Hard coded m_window to start with client/server widget width...also
removed unnecessary slots from MainWidget.
Changed setup to be tab-based

This way is much simpler and allows user to access both client and
server without having to open a new instance. A starting screen could
easily be put back in if needed.
Window now non-resizable by user
Added a window icon, added more hard-coding.

QTabWidget sucks.
Added a mask for the IP address line
Added Close action to File menu

demonstrates functionality of qmenubar
Updated gitignore to ignore VS files