Add {{intlTime}} helper

This helper delegates to `{{intlDate}}`, but will first reference any String named `format` from `data.intl.formats.time`.

Since the pre-defined/named formats are used by `IntlMessageFormat` — which distingishes between `"date"` and `"time"` — we need a separate time helper to match.
Merge pull request #43 from ericf/time-helper

Add {{intlTime}} helper