There were some timezone issues especially concerning daylight saving time (DST).
We should not rely on timezone offset since this will change due to DST.
Instead determine the users timezone (using jsTimezoneDetect therefore) and
then using this via moment-timezone.
This commit changes poll model. It drops timezoneOffset and adds timezone as a new property.
It's not tested yet against polls created before without timezone property. This has to be done before merge.
Also we should consider using ember-moment template helpers instead of our own formatted-date helper.
Ember.ObjectController was proxying model properties to controller. Ember.Controller which should be used is not.
Therefore we have to define if it's a property of controller or model.
Also added two more tests:
* anonymous participation
* do not force an answer for all options
