Lock offline template cache to a particular index hash

This gives us the ability to rebuild old versions of
activator. It means that for example our CI won't start
to fail as soon as someone updates one of the featured
templates.

Initially locking to the hash that shipped with
Activator 1.2.3
Fixed log message from java version check that said local when it wasn't
On publish and S3 upload, complain about outdated cache hash
Move the check for latest hash to after publishSigned

Apparently the before-publish hooks I was using are needed
for offlineTests and integrationTests too.
Merge pull request #607 from typesafehub/wip/havocp-lock-template-cache

Lock down the template index version