Add counting of total video frames to outputs

Before it would assign the encoder/media callbacks directly to the
output's callbacks, so instead of doing that, it now goes through
intermediary functions for the sake of counting the frames.
Add statistics functions to outputs

Total bytes, total frames, and frames dropped.  Total frames is
generated automatically, but total bytes and total dropped frames are
returned via callbacks.
rtmp-output:  Add statistics callbacks

Add callbacks for total bytes sent and number of dropped frames
Add function to main window to query CPU usage
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 in to its own derived class.