BLTI-269
Add Splash Capability to the Basic LTI Portlet

Adds a splash configurtation to the External Tool portlet and the following two 
fields are also available for any LTI Portlet tool registration: 

sakai.basiclti.overridesplash=<b>You are leaving Sakai to visit an external site. Have an override day.</b> 
sakai.basiclti.defaultsplash=<b>You are leaving Sakai to visit an external site. Have a default day.</b> 



git-svn-id: https://source.sakaiproject.org/svn/basiclti/trunk@128672 66ffb92e-73f9-0310-93c1-f5514f145a0a