Add possibility for users to disable integration for themselves

[bugy]

It would be nice, if user could disable(/enable back) getting JIRA information message. (Sometiems messages can look quite spammy)
Also, some people would like not to be "listened" by external software. So it should be a possibility to disable rocket cat from reading that users' messages.

As a proposed solution, a user can send some message to Rocket.cat bot. Like "@rocket.cat jira ignore" or "@rocket.cat jira disable"

[gustavkarlsson]

An enable/disable feature is a good idea, but it requires persistent storage, so I'll have to look into using a database in that case.

When it comes to listening to users, I don't think it makes any difference since the messages always go to the app anyway. If it's actually reading the message or not doesn't really matter...