Add `handlebars` module

 * Needed for https://gerrit.wikimedia.org/r/#/c/127865/

 * Also removes extraneous modules from
   https://gerrit.wikimedia.org/r/#/c/106554/

Change-Id: I0ebb75e293d6ab01bd48e574544e1404b0c15c25
Merge "Add `handlebars` module"