therefore we have to duplicate it in store:
* encrypted for to serve for clients (encryptedExpirationDate)
* unencrypted for server to check if it's exceeded (serverExpirationDate)
serverExpirationDate should never be send to client
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.
