travis CI: run doctests
tests: quaternion doctest fix

Don't use functions we don't have.
move modules that require ROS to their own sub-package
make pymvg.extern.ros sub-package
move OpenCV requiring modules to own directory
make pymvg.extern.opencv sub-package
update for new ROS files location
fix missing import
update for new location of opencv-requiring code
test coverage: remove configuration that did nothing
travis CI: do not run external tests
travis CI: clarify argument to nosetests
tests: increase coverage
tests: increase coverage
remove unused code
tests: move test

test load of MCSC test data doesn't need MCSC installed.