Issue warning if `zilla dump` version not aligned with engine files version

[jfallows]

Include zilla version in engine info file, alongside worker count, so that zilla dump can issue a warning if there is a version mismatch.

Under typical circumstances, when running zilla dump in the same context as zilla start the version will be identical.

However, when analyzing an archive of the zilla engine directory from another system, this will help to make sure the correctly typed structures are being applied to the engine data, etc, in case the archive is from an older version.