Timezone support

[L1Cafe]

While I do try to stick to UTC as a timezone, I think Vigil would do a better job if it had the possibility of changing timezones.

As this isn't in the documentation, I assumed there's no possibility to change timezones.

A few ideas here:

• Timezone should change depending on the visitor (not sure if there's a standard way to do this, but perhaps https://stackoverflow.com/questions/6939685/get-client-time-zone-from-browser that should help).
• There should be a way to set up a different timezone for notifications (if the administrator lives in Beijing, they probably don't care about UTC notifications).
• Lastly, if timezone cannot be detected, it should resort to UTC (as opposed to resorting to the administrator's timezone).

[martin-micimo]

I am not a rust programmer, but I think this could be achieved by replacing time::OffsetDateTime::now_utc() with time::OffsetDateTime::now_local() in:

https://github.com/valeriansaliou/vigil/blob/master/src/aggregator/manager.rs#L336

Do not know how to change the Format in https://github.com/valeriansaliou/vigil/blob/master/src/aggregator/manager.rs#L54 properly, so it displays ok.

And I do not know what kind of side effects this would have in the checking.

But I would like to have that enhancement too.

Can confirm, that it still shows UTC in the Status page if you set the TZ environment to a different timezone on the server.