Add an end state automatically when an exploration is created.

[GoogleCodeExporter]

Currently when an exploration is first created it has just a starting state. In 
order to end the exploration the user has to create an additional state and 
give it the END interaction.

This proposal (made by Sean) is to begin with both the starting state and an 
ending state, the latter of which will have the END interaction already 
selected. That way users just need to link to it in order to end the 
exploration.

Original issue reported on code.google.com by jacobdav...@gmail.com on 3 Aug 2015 at 5:05