BlankPackageInstaller: Add internal flags from AOSP

The INSTALL_* flags are not in the SDK so we will define them locally.
libs: Add android-support-v4.jar dependency, rev 19
libs: Add PackageManager callback stubs

In order to receive callbacks from the internal PackageManager APIs, we
need to extend a few abstract "Observer" interfaces that aren't in the
SDK.  These were extracted from framework.jar / framework.odex in the
ICS emulation image.
Add infrastructure for Ant builds
BlankPackageInstaller: Use reflection to call internal APIs

This eliminates the dependency on building against a modified SDK.
BlankPackageInstaller: Check permission when setting up reflection

Make a test call to installExistingPackage() to see if the
PackageManagerService throws a security exception.  If so, tell the
caller that we don't have permission to call installPackage() and
deletePackage().
Add build instructions and travis-ci script
BlankStore: Fall back to intents on non-system installation

If BlankStore isn't installed under /system, it cannot use Android's
internal APIs to quietly install/uninstall packages.  Instead, it must
go through the interactive dialogs provided by the system.
BlankActivity: Prompt user to create account if needed

If the user has not yet created an account, redirect him to the account
creation activity on startup.

FIXME: what to do if they hit Back instead of creating an account?