[FEATURE REQUEST] Show snackbar after adding a member to a space

[jesmrec]

In order to have a better UX, a notification snackbar when user is added to a space will let users know whether the adding operation was successful or not.

It's helpful when the added member is sorted in the bottom of the list, and the bottom is out of the screen. In this case, after clicking on Invite, user will see neither changes nor confirmation -> confusion.

Same would apply to edit and remove member

TASKS

• Research (if needed)
• Create branch feature/show_snackbar_after_add_member_operation
• Development tasks
  • Show snackbar after add member operation
  • Implement unit tests (if needed)
• Code review and apply changes requested
• Design test plan
• QA
• Merge branch feature/show_snackbar_after_add_member_operation into master