Don't allow people to post +1 on an issue tracker (BB-8952)

This is really very annoying, because everyone who posts "+1" does not really help with a constructive comment, but keeps spamming all the watchers' email inboxes.

Solutions that I suggest:

1. Don't allow comments less than N characters in this tracker
2. Deny comments consisting only of "+1" (stripped of whitespace) with an error message, explaining that user should use voting feature
3. Automatically convert "+1" to votes

In my personal opinion, the third solution is the best.