add revoke action to before_action ":assign_target_user"
add form button to revoke admin from member
add css for revoke admin button
add message for revoking admin from a member
controller spec for revoke admin from a member
feature spec for revoke admin from a member
change css for buttons to be within the box.
change unless to if-else for the condition of member.configurable?.
add message in English for revoking admin from a member.
change put to patch