Added functionality to edit a item

Created a second activity which gets called and once edited. The contents are saved to the file again.
Adding files missed in previous commit for editing functionality.
Adding support for sqlite database based saving of todo list.
Added README and example screenshot.

Made a first cut of README.
Created a gif of the demo of the app.
Merge pull request #3 from vishalpatel/ShouldDo

Sqlite backed data storage for Notes.