Payment prefs: use relative local and ISO 8601 dates

[ayumi]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Test Plan:

• Add moment.js which localizes time/date things

Fix #4294

Auditors: @jkup @mrose17

Test Plan:

1. In Prefeences > Payments, see Status and look for the "Next contribution: in {n} days".
2. In Payment history, check that contribution dates are in ISO 8601 format (YYYY-MM-DD).
3. Also look near the bottom for "Next contribution :in {n} days".
4. Change Browser language in General then restart browser
5. Go to Payments, see Status and find localized "in {n} days string"

[mrose17]

lgtm: please commit.