PEEK: Sensors improvements

- Bring some fixes to the algorithm thanks to @D4rKn3sSyS
- Cleanup

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
DocumentsUI: Handle NPE gracefully

Cherry-picked from OmniROM.

http://jira.omnirom.org/browse/OMNI-956

Change-Id: I8d50d71a9c91486dfc9e5da01538c6b5a626f054