Edit gitignore

Exclude OS-X related hidden file (.DS_Store)
Edit gitignore

Exclude OS-X related hidden file (.DS_Store) and Eclipse build files (.metadata and appcompat_v7)
First draft of UI

This minimal version provide just a string, a button and a call to the default android camera app.

Next steps:
- Add a call to a user defined function (the core function)
- Output the result of the core funtion to a second activity