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
Docblock should mention that it might return `None`.