added heka-py and heka-py-raven integration

* added dependency on raven 3.4.1 and heka-py-raven 0.7
* dropped all instances of the standard python logger for ichnaea
* added logging for timers around requests, tasks
* added logging for items uploaded per submit
* a sample hekad.toml file is included that will work with heka >= 0.4.1
* logger configuration for waitress has been removed

This should resolve #13 and #14 as raven will handle exception capture into Sentry for us