Move jetty-related tasks to deploy/staging.rb

We use jetty in staging, but tomcat in production. Jetty-related tasks
need to be constrained to the staging environment.  In this commit,
the jetty-related before/after callbacks are relocated from deploy.rb
to deploy/staging.rb
Merge pull request #75 from NYULibraries/chore/update-deploy

Move jetty-related tasks to deploy/staging.rb
[Finishes #73890674]