Rude and inaccurate email sent automatically to team members (BB-7971)

Steps to repro:

• create a team and a group within it that has write permission and the ability to create new repositories
• invite some members to the group
• remove the ability to create new repositories from the group

Result is that all members of the group are sent an email which says, in it's entirety:

From: Bitbucket <notifications-noreply@bitbucket.org>
Date: Mon, [DATE]
Subject: You are no longer a member of [TEAM NAME]
To: [TEAM MEMBER]

Your membership of the [TEAM NAME] team has been revoked.

This message is also plastered all over the team's activity log once for each team member.

You then have to re-assure your team that their access has not in fact been revoked.

Expected behavior is that team members would be notified of the specific change in their permissions. It would also be nice if in the activity stream, there was only one message for the group's permission change rather than a steam of messages for each user.