split !status into smaller parts

You should be able to call !status plugins, !status load or
!status gc independently
fixed syntax error on exception
fixed logic where 3to2 would run when running 'python setup.py develop' on python3
updated existing tests to pass
added new !status subcommand tests
re-added and reworked the html-im templates for !status output
corrected a couple of broken tests
as suggest, I've simplified the 3to2 check when running 'setup.py develop' on python3
Various bugs / imperfections spotted by pycharm.
no imp under PY2
Merge branch 'various-refactorings' of github.com:gbin/err into various-refactorings