Adding selenium tests for inbox/sent notifications (Bug #1055206)

Tests include:
- Sending a message as admin user to user.one
- Checking sent box as admin that message exists
- Deleting message from sent box
- Checking inbox as user.one to see if message is received
- Deleting message from inbox

Change-Id: I78fa01424ab7364ac1b7673d9f190bcea9b5a2a1
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>