Add support for connecting multiple Slack teams

[smartym-sv]

In the plugin settings allows to add a few Slack teams (hooks, teamName)
Add custom field team name (preferable dropdown) with team name selection

Thank you in advance.

[avkoval]

Is this a dup of: #17 ?

[avkoval]

So, yes, I've tried solution explained in #17 and it works well for me. So, @smartum-sv I belive we can close this, as its being addressed already