indigo: use Python 2 rather than Python 3.

Since most packages are unlikely to be Python 3 ready before the
next ROS distribution, we stick to Python 2.
Update README.md (a word on Python).
Add helper script to check patches.
indigo: add ros_core.
indigo: add ros_base.
indigo: add robot.
indigo: add viz.
indigo: add desktop.
indigo: add perception.
indigo: add simulators.
indigo: add desktop_full.
hydro: update desktop_full.
indigo: update desktop_full.
python2-bloom: update.
Dependencies udpate.
hydro: update desktop_full.
Merge branch 'arch' into chakra

Conflicts:
	README.md
	dependencies/python2-argparse/PKGBUILD
	dependencies/python2-rosdistro/PKGBUILD
dependencies: add ogre-1.8
gazebo_plugins: replace ogre with ogre-1.8
fix python names