Long Press to Save/Share

This is one of those features that may not be something you're looking for, but I thought it was useful

All of the code for the activity views is now stored in one place in the singleton (you were duplicating it for the web view and for the reader view, and I didn't want to duplicate it a third time in your code).

When you long press on any cell in the MAMViewController it'll bring up the activity view, so you can email, open in Safari, send to Pocket, etc without needing to load the story

![activity-view](https://f.cloud.github.com/assets/516458/772641/b3415ee8-e914-11e2-88b1-5976c431ab76.gif)