start DU common sepolicy

Credits to OmniROM for being the medium from which these commits come
from.. and credits to the original authors of each of these commits:

 sepolicy[1/8]: start OmniROM common sepolicy

 sepolicy[2/8]: exFAT Support

 sepolicy[3/8]: Fix asec mounting

 sepolicy[4/8]: treat fuseblk as sdcard_external

 sepolicy[5/8]: allow installd to query ASEC size

 sepolicy[6/8]: allow vold to create files on external sdcard

 sepolicy[7/8]: allow vold to mount ext4 sdcard

 sepolicy[8]: Add specific file_contexts

Change-Id: I48e2472830a28bdc57d7f50247275e25aa39ddea