Implement status bar

The status bar now displays:
 - Auto-reconnect information (reconnecting and reconnect success)
 - Dropped frames (as well as percentage of total video frames)
 - Duration of session
 - CPU usage of the program
 - Kbp/s

The OBSBasic class is getting a bit big, so I separated out the
status bar code to its own class derived from QStatusBar.