Remove clear_output timeout callback in favor of fixed height
Removed ability to clear stdout and stderr individually.
Added wait flag to clear_output.
Don't preserve height when clear_output(wait=False) is called
Updated clear_output animation example nb
Added wait=True to a couple more clear_output calls.
Added clear_output changes
Added double backticks around wait
Merge pull request #4229 from jdfreder/clearoutput

Clear_output: Animation & widget related changes.