Creates 2 new types:
- asec_apk_file : files found under /mnt/asec
                  when the asec images are mounted
- asec_image_file : the actual encrypted apks under
                    /data/app-asec

Change-Id: I963472add1980ac068d3a6d36a24f27233022832
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>

New property_contexts file for property selabel backend.
New property.te file with property type declarations.
New property_service security class and set permission.
Allow rules for setting properties.