Determine if we need to fire a terminated event in the receiving browsing context(s) #374

Currently, the steps for terminating a presentation don't fire a terminated event on connections held by the receiver. If the process of closing the receiving browsing context could allow script to run, then we should consider firing this event (on the top-level or nested browsing contexts). Doing so may be redundant with the 'beforeunload' event however.

Reference material:

• Closing a browsing context
• beforeunload event
• unload event