Silent dependency on python-dateutil

[mkorvas]

Dependency on python-dateutil should be defined in setup.py.

Upon installing hamster-bridge with pip, I observed the issue as can be seen below:

$ hamster-bridge jira
Traceback (most recent call last):
  File "/home/matej/.virtualenvs/2.7-hamster/bin/hamster-bridge", line 11, in <module>
    sys.exit(main())
  File "/home/matej/.virtualenvs/2.7-hamster/local/lib/python2.7/site-packages/hamster_bridge/__init__.py", line 27, in main
    (lc.short_name, lc) for lc in [import_listener(l) for l in LISTENERS]
  File "/home/matej/.virtualenvs/2.7-hamster/local/lib/python2.7/site-packages/hamster_bridge/__init__.py", line 12, in import_listener
    mod = __import__(name.rsplit('.', 1)[0])
  File "/home/matej/.virtualenvs/2.7-hamster/local/lib/python2.7/site-packages/hamster_bridge/listeners/jira.py", line 16, in <module>
    from dateutil.tz import *
ImportError: No module named dateutil.tz