Review translated strings.

- Include trailing colons inside translated strings because some
  languages (eg. French) need a space before the colon.
- Normalize capitalization (title-style didn't seem warranted and looked
  weird in some cases).
- Normalize quotes (not very useful, but we had a random mixture of
  single and double quotes).
- Remove msgstr from the English po file because they're identical to
  msgid by definition.