Make "Preferred Timezone" a reserved field in the pod UI

[mariadimou]

Sorry I was intending to open this enhancement issue for over 3 months already.

Background: Seeing several iterations in the gitter channels often verifying "at what time the meeting will take place" I suggested in the gitter channels, back in March, to introduce field Preferred Timezone as a field on one's pod profile.

@timbl commented in https://gitter.im/cern-solid/community#:

Timezones in wikidata

Offset

@timbl also commented on Apr 08 23:20:

Though it has GMT as UTC+12 which is very wrong So it gives you the name of the TZs and the offsets but doe not sort out whether daylight saving is on or off