envcan: remove timezone methods.
Convert reported date timestamp to a useable string and use this to determine period of day, we assume if it's 4pm or greater then nightfall may be starting (in some places of the world).

This adds some private methods night() and periodHour().
We also have to do some ugly a handling for various condition/forecast types.
We use m_conditionNightList['condition_or_forecast'] and set this to a valid icon using the enumerated values.

Surely there's a better way?