Sending mails to groups

As an Admin I'd like to be able to send mails to the groups of users so that they can get some general announcements

Use case's flow description:

1. Admin goes to Poulpe -> User Groups and calls context menu for any group(right click on any group).
2. Admin selects "Send message" item from context menu.
3. New modal dialog box appears on the screen with title "Send message to #GROUP_NAME members".

Functional requirements:

• The dialog box should have next components:
  a) Message topic - to define message's topic
  b) Message text - to define message's body
  c) Send button - to send mail to group members
  d) Cancel button - to cancel e-mail sending and redirect to Poulpe -> User Groups

• After sending the message there should be notification for users, for example "The message have been successfully sent".
  If there are no users in the selected group, the error message should be shown, for example "There are no users in the selected group"

Acceptance criterias:

• The context menu for any group in Poulpe->User Groups should contain item "Send message".
• After repeating all steps, described in "Use case's flow description", all members of selected group have to receive letters on their e-mails with created message.