Fix resource code and version attributes

Create a new package setting object for updated system apps rather than moving
around the same setting. This updates the resource, code and version correctly.
For updating system packages, disable the package first which removes the entry
from internal structures, create a new package setting, add it to list of user id's
then rest of installation steps, kill the process if needed via ActivityManager
then add this setting if everything was successful. This also fixes issues with
updating values prematurely.

When a new version of system package is available via OTA, just physically remove
entries for pkg. Note that the component and other info will be eventually updated
later on when scanning the package.
Also move certificate verification slightly ahead before scanning packages.

Some null checks

New api's in ActivityManager to kill an application pkg before finishing installation