steal-bundler should print some logs

[nlundquist]

It's not clear to the user of steal-bundler what it's progress is, what modifications it's making, or that it's running at all during a steal-tools build.

When debugging an issue with steal-bundler I expected it to have already run by the time steal-tools wrote the bundles, as from the steal-tools logs it appears like the build is complete after the bundles are written. I wouldn't have had this misconception if there had be logging indicating that asset bundling was occurring after the JS bundles are written.