add custom actions

[ryanjblajda]

allow for a custom action string, which would include additional content to be attached to the cards content, either to notify team members or for some other reason

[ryanjblajda]

being able to tag someone seems to be quite a difficult lift, so maybe just adding custom content. or nixing this feature entirely.

[ryanjblajda]

progress, tagging is now achieved using the notify_team_members array in the custom_actions object