make SignApk do zip alignment

When signing an APK, make the SignApk tool align the stored entries to
(by default) 4-byte boundaries.  This obviates the need to run the
separate zipalign tool, which currently does this job.

The alignment byte count can be specified with the -a option.  OTA
package signing (with -w) never does alignment.

The order of files in the output APK is changed so that all stored
files come first in the output, followed by all non-stored files.
This is not expected to have any impact in practice.

Change-Id: Iaeef89b2a7283e25fadb99c0a0f0641f682d76b8