Allows listing organizational folders

[romank0]

Organizational folders are provided by Branch API Plugin.
They do not have status and color is not returned for them so exception is raised.

$ bin/python -m jenkins.get_jobs_xml
Traceback (most recent call last):
  File "~/.pyenv/versions/2.7.10/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "~/.pyenv/versions/2.7.10/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "~/workspace/develop/jenkins/get_jobs_xml.py", line 22, in <module>
    all_jobs = jenkins.all_jobs()
  File "~/workspace/develop/lib/python2.7/site-packages/autojenkins/jobs.py", line 157, in all_jobs
    return [(job['name'], job['color']) for job in jobs]
KeyError: 'color'

This commit changes all_jobs function so it skips them by default.
Additional option allows to include them.

This implementation filters by presence of the color parameter in a job. Alternatively we can filter by class name of the job.

[txels]

Ah cool, thanks for this @romank0! Nice to see you around these parts.

[txels]

This has been released as v1.1.1