Fix performance issues: IAAS-1880

	Unload the DOM of steps which are not displayed fix a lot of watch and
	dirty checking listeners.
Public is now the first tab on launch instance select source
FIX IAAS-1881 Better message for network selection

	Add understandable help message for network list and security group list
	if no items are selected, show the help message for user,
	to get more understanding.
Add closing cross on modal