Refactor - enhance maintainability

[jubeira]

From https://github.com/Intermodalics/ros_android/pull/47#pullrequestreview-180899501 (summary):

• [x] Use wstool to get system libraries.
• [x] Apply patches automatically.
• [ ] Detect automatically which script to use (with or without toolchain) to create simpler build rules for libraries (libraries still need to be listed explicitly).
• [x] Rename build_cpp.sh to build_catkin_workspace.sh or build_ros_stuff.sh (for consistency with get_ros_stuff.sh).
• [x] Review and simplify scripts; place exports in config.sh and add some documentation.

[ivanpauno]

"Apply packages automatically" means "Apply patches automatically", right?

[jubeira]

Yes; thanks for the observation, edited now.