Ensure an error message in LBaaS is displayed once.

Fixes bug 1160920

This commit also changes the following:
- Fixes wrong messages like 'Added Monitor "Add Monitor".'
  in AddMonitor and AddMember.
- Moves validation for cookie_name in handle() in AddVip class
  to clean() method.
- Improves an error message for member check in AddMember action
  and removes an unused member check in handle().
- Make LBaaS forms modal.
- Changes all lowercase and capitalized "vip" to "VIP".

Change-Id: I96f76d2f2177c0789ae4e939484f3965ba93d86c
Merge "Ensure an error message in LBaaS is displayed once."