MTP and media provider support for multiple storage devices:

- MTP support for multiple storage units

- Add storage_id column to media database for MTP storage ID

- Add framework resource for defining mount points and user visible descriptions
for multiple volumes

- Clean up locking in MtpServer JNI code

Change-Id: Iffb66ed156ef5bc80b14228af78fbacee7734360
11 files changed