Reminders Changes/Improve Reminders UI

[kchia]

• [x] default date picker to 3 months
• [x] add back frequency for reminders
• [x] on reminder date picker, say: "that's 90 days from today"
• [x] Add a "Change Date" button.
• [x] Hide the date input field after reminder has been set.

[dsernst]

@kchia: looks like all 5 of those TODOs are checked off, can we close this?