cli_utils: add module with commonly used funcs

This pull request creates a new module in the `cli_utils` package which provides some commonly used CLI related functions. In this pull request I have added:

- `extract_jobs_flags` which extracts job flags from make arguments
- `extract_argument_group` which extracts groups of arguments from command line arguments

Both new functions have tests and documentation. Preview documentation is available here:

http://osrf-pycommon.readthedocs.org/en/cli_utils_common_module/cli_utils.html#module-osrf_pycommon.cli_utils.common
That's a good question, I need to look into how other incantations of this function are being used elsewhere (like in catkin) and see what the use case actually is. It may make sense to capture and pass along unused tokens.