Timezone localizations

[krazkidd]

Timezone localizations would be helpful.

Tasks

• [ ] Default to system timezone (fallback to Eastern Time per the Exchange)
• [ ] Save timezone and time display preferences to config file (to allow hand-editing--no need to provide a preferences dialog to complete this issue)
• [ ] Localize announcements
• [ ] Localize maintenance windows (and add to Announcements dialog)
• [ ] Localize exchange daily schedule
• [ ] Localize any other market/portfolio API data added since this issue was created

Dependencies

• [x] #37
• [x] #41
• [x] #44

[krazkidd]

We might add a special widget for showing localized times like we do for currencies (see #42).