no need to extract the (huge) nativve lib to the device's filesystem on
newer android versions (Marshmallow and later) - can access the .so from
within the apk if it is uncompressed.
While the standalone apk will be larger, the delta-update mechanism of
playstore can be more efficient, so you get:
* faster installation (since the file doesn't need to be extracted)
* less disk usage on device (for same reason)
* smaller delta-updates for playstore

drawbacks
* larger standalone apk
* on older android version more storage needed (the increased size of
the standalone apk), as those will still extract the native-lib

Unfortunately uncompressed it exceeds the current maximum size for
single apk files in playstore (100MB), so cannot use for release-builds

also revive installLocation attribute to allow installation on external
storage and move from manifestPlaceholders from defaultConfig to release
buildType (as otherwise gradle complains about having "Multiple entries
with same key")

Change-Id: Id07ac9c144886bb89abaf7b5b4bc7bd548f27247