Cryptocat 2.1.21

- Cryptocat for Firefox now only supports Firefox 21 and higher. This
allows us to remove some outdated hacks that were necessary to allow
older versions of Firefox to support Cryptocat.
- Added Ukrainian translation.
- Small fixes were made to the Spanish translation.
- The authentication interface has been updated to clarify that
question-based authentication is for private OTR chats only.
- Fixed a bug that would allow clients with malformed nicknames to
cause a crash in other Cryptocat clients in a conversation.
- Fixed a bug that would allow clients with malformed nicknames to
secretly join a Cryptocat conversation and obtain ciphertext. These
clients would not be part of the conversation however and would not be
able to obtain plaintext.
- Fixed a bug that wouldn't allow non-latin characters in
question-based authentication.
- Fixed a bug in Cryptocat for Firefox that would not add a Cryptocat
button to the Firefox toolbar.
- Fixed a bug that would not allow the user to scroll up for a few
seconds if they receive too many new messages in a short period of
time.
- Many small improvements were made to the user interface.
- Many improvements and optimizations were made to the Cryptocat code.
- Updated Cryptocat dependencies to their latest versions.