Make scheduler timezone aware

[tijlleenders]

Scheduler input for calendar start/end is timezone aware.

This timezone is used for the purposes of calculating repetition boundaries like "daily" and "weekly".

[thinkrapido]

The scheduler should be relying only on UTC. With this in our hand, we can have cross goals and participations form other users of the app possible later on in the development of the zinzen app.

[tijlleenders]

@thinkrapido
Agree that when in the placing phase - everything should be based on or converted to UTC.
For calculating the appropriate timeline though - we should know which timezone it is in.
A daily standup with your team in the UK at 8 should always be correctly scheduled - no matter where you are in the world.
This doesn't mean you want your breakfast at 8 UTC when travelling to China...

Anyway - this is way in the future - and not a prio right now.