Create new "slider_training" app

[ianchadd]

Create a new app that does the following:

• Takes the place of pt1 (i.e. if there is anything to pass from pt0 to pt1, slider_training should function in a similar way)
• Split Intro from pt1 into 4 separate pages. One for each of the Examples and one with just the comprehension questions that are at the end of the examples in the current Into template.
• It should function similar to pt1 in that it should expect pt2 to come after it and should save/pass along any relevant variables

[mcdaij]

I'll get this tested and submitted for you by Thursday morning at the latest, hopefully Wednesday morning.