Methods to calculate user and external disk usage.

Add method to calculate user disk usage, which will be faster than
making a Binder call for every single appId under a user.  Add method
to calculate external disk usage, which uses file extensions to track
usage with "audio", "video", and "images" categories.

Add script to generate optimized file extension matcher logic.

Start measuring internal and external storage space separately; new
GIDs are coming in a future CL.  Pass down all package names, inodes,
and code paths, since shared UIDs host more than one.

Test: builds, boots, stats are consistent
Bug: 27948817, 32206268
Change-Id: Icb9843ac5159e0e5f1503d9b64e0bcae407e1a5d