Add `translate_emoticons` to `prop_types` and `expected_keys`.
Furthermore, create a emoji-translating Markdown inline pattern.
Also use a JavaScript version of `translate_emoticons` and then use
this function during Markdown previews and as a preprocessor. This
is only needed for previews, because usually emoticon translation
happens on the backend after sending.
Add tests for emoticon translation, a settings UI, and a /help/ page
as well.
Tweaked by tabbott to fix various test failurse as well as how this
handles whitespace, requiring emoticons to not have adjacent
characters.
Fixes#1768.
Marco Burstein