DO NOT MERGE. Add package-name-prefix blacklist for location updates.

The Settings.Secure value locationPackagePrefixBlacklist and
locationPackagePrefixWhitelist contains comma seperated package-name
prefixes.

Location & geo-fence updates are silently dropped if the receiving
package name has a prefix on the blacklist. Status updates are
not affected. All other API's work as before.

A content observer is used so run-time updates to the blacklist
apply immediately. There is both a blacklist and a whitelist.
The blacklist applies first, and then exemptions are allowed
from the whitelist. In other words, if your package name prefix
matches both the black AND white list, then it is allowed.

Change-Id: I4ea2ad56fa6bd75d32151bc250ac25c26a5777c4