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.
"In this paper, we will describe one solution for hiding of private data, including an open source implementation of that solution, for the popular mobile operating system, Android."

Also: 
"Here we only focus on preventing sensitive files from leaking with casual searches." (not sure about "casual searches" as it might not be clear yet what we mean. Perhaps define it?)