First draft of the introduction

Rewrote the introduction as a usecase.

Pulled the introduction into a separate file.

This is a first draft but thought I'd get out a general idea of the introduction I had out as soon as possible.
It probably needs some changing yes now that I think about it. But basically it's supposed to be the switch from introduction to what is in the paper.
I think it's useful to say that we will describe a solution to hide data, and an implementation in android. Followed by the structure?