Default to UTF8 resources when packaging with aapt

This change makes it so with API level 7 and above all resources will be
packaged in UTF-8 format. Any minSdkVersion level that is named will also
have resources packaged in UTF-8, because it is assumed that previous
releases will only be rebuilt with their proper integer number and only
future releases will temporarily have names.

Change-Id: If5d1ee5e48fbaf31798816b068ac44b14a93121b