Add Math display support for qtconsole
Initial messing around.

Latex tab completion will have to be done outside the normal
completer logic as the completer line splitting logic uses
\\ as a special character to split lines on. I probably want
to put the latex completions first and it if finds any matches,
don't do any other completion logic. The only issue is that might
short circuit dir/path matching on windows. Hmmm.
Adding autogenerated latex_symbols.py.
Adding regexp for unicode identifers to CM mode.
Initial implementation of latex->unicode completer.
Cleaning up and only doing latex completion for python 3.
Adding partial latex completions.
Adding tests and limiting CM mode to python 3.
Adding latex_symbols.ipynb.
Adding script to generate latex_symbols.py.
Updating gen_latex_symbols.py
Handle sessions where the kernel has been killed
Fix failure message for tests
Fix 404 error when accessing nonexistant session
Correct comment
Add tests and fix some issues

Tests taken from #6360
Pull docs on defining magics out to customisation section
Fix some doc build warnings
Initial version of textbox celltoolbar ui element
Merge pull request #6425 from takluyver/docs-separate-defining-magics

Separate doc on defining magics