Do not create a mention embed if the message contains a certain keyword

[dericksonmark]

Purpose

Adds #14.

Approach

If forbiddenTicketText (default is !nm [no mention]) is set in default.yml, MojiraBot won't create a ticket embed if the message contains the forbidden text.

[violine1101]

To provide a bit of context, I've created this issue because the way in which MojiraBot creates ticket embeds is somewhat obtrusive (only mentioning a ticket suffices to trigger the bot). Thus I explored some solutions to this problem, one of which was to have some keyword that disables mentions.

However, I think by now (1.5 years later) I think the better option is just to only trigger the bot if the ticket ID is prefixed with !, like how most bots do it. That's just way more user friendly.

In this case, this feature would just not be needed at all anymroe (which would be good because I don't really like MojiraBot becoming more and more complex)

Wanted to bring this up in Discord already, but haven't come around to it.

[violine1101]

Perhaps in general, in the beginning of the project I used the issues here as an idea dump and not as "something that we need". I should go through all of that and sort out what is actionable and what isn't.