setup.py: Added gevent dependency
tracking: Converted tracking daemon from twisted to gevent

gevent is supposed to solve our concurrency problems with SQLAlchemy.
setup.py: Removed Twisted dependency
tracking: Moved app instance into "runserver" command
tests: Added "app_class" fixture

see http://pytest.org/latest/unittest.html#mixing-pytest-fixtures-into-unittest-testcase-style-tests
tests/tracking: Adjust TrackingServer tests to new method names
tracking: Use new log() function instead of print

log() flushes the stdout directly, so that runit can timestamp
the message correctly
tracking: Extended logging
Merge pull request #343 from Turbo87/gevent-tracking

Converted Live Tracking Daemon from Twisted to gevent