Normalize Timezones

[joshreisner]

this PR allows sites to leave out the data-timezone and have meeting times translated into the user's timezone

meetings would be required to provide their own timezone in the right format

it would not have TSML support initially, since TSML:

• doesn't store timezone information for meetings
• always specifies timezone in its embed shortcode

closes #248

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[joshreisner]

i have two concerns so far about this PR:

1. there's currently no outward indication that the timezone has been translated. i added times to the meeting names, but presumably most sites would not do this. i'm not sure how important it is for online meetings, but for in-person ones (if i'm planning a trip, say) then this should probably be flagged in the interface somewhere

2. this makes it so if you do specify a timezone the times all get normalized to that timezone. this could present a problem on a site that currently displays meetings across a range of timezones such as Continental European Region (they are currently not using TSML UI, but maybe we should contact them about this change)