Update USB configuration and set default to MTP, ADB

Media Transfer Protocol allows shared access to the SD card by
the PC and Android OS simultaneously. It's supported on Windows
and Linux, so let's use it instead of USB Mass Storage mode.

Change-Id: I858699585ac4a3102ff473fd662fdefbca00f6b4
Update storage configuration & development settings

* Add debugging properties
* Allow mass storage mode
* Update default USB configuration (still using mtp,adb by default)

Change-Id: Ibef617fd0a56c7f1d46092114f65fa867298378e