Fix Download document button on Project Revenue Sheet

Steps to Reproduce:
Using the Template Rendering Samples addon in Web UI:

• Within Workspaces, create a Portfolio Container document.
• Withing the Portfolio Container, create a Project Document.
• Click on the Generate Project Revenue Sheet.
  => [Poorly formatted] PDF is generated.
• Click on the download button underneath the PDF preview.
  => File is not downloaded.
  => No errors in browser console.
  => Warnings in server log (though not sure if it is related):

  2018-12-07T16:06:06,271 WARN  [http-nio-0.0.0.0-8080-exec-4] [org.nuxeo.elasticsearch.io.marshallers.json.AggregateJsonWriter] Could not resolve field picture:info.colorSpace for aggregate color_profile_agg
  2018-12-07T16:06:06,271 WARN  [http-nio-0.0.0.0-8080-exec-4] [org.nuxeo.elasticsearch.io.marshallers.json.AggregateJsonWriter] Could not resolve field picture:info.depth for aggregate color_depth_agg
  2018-12-07T16:06:06,271 WARN  [http-nio-0.0.0.0-8080-exec-4] [org.nuxeo.elasticsearch.io.marshallers.json.AggregateJsonWriter] Could not resolve field file:content.mime-type for aggregate system_mimetype_agg
  2018-12-07T16:06:28,381 WARN  [http-nio-0.0.0.0-8080-exec-1] [org.nuxeo.elasticsearch.io.marshallers.json.AggregateJsonWriter] Could not resolve field picture:info.colorSpace for aggregate color_profile_agg
  2018-12-07T16:06:28,381 WARN  [http-nio-0.0.0.0-8080-exec-1] [org.nuxeo.elasticsearch.io.marshallers.json.AggregateJsonWriter] Could not resolve field picture:info.depth for aggregate color_depth_agg
  2018-12-07T16:06:28,381 WARN  [http-nio-0.0.0.0-8080-exec-1] [org.nuxeo.elasticsearch.io.marshallers.json.AggregateJsonWriter] Could not resolve field file:content.mime-type for aggregate system_mimetype_agg
  2018-12-07T16:06:29,746 WARN  [http-nio-0.0.0.0-8080-exec-4] [org.nuxeo.ecm.platform.tag.FacetedTagService] Getting tags on /default-domain/UserWorkspaces/admin848/Favorites failed since NXTag is missing on Favorites document type. This operation will be ignored.
  2018-12-07T16:06:29,752 WARN  [http-nio-0.0.0.0-8080-exec-30] [org.nuxeo.ecm.platform.tag.FacetedTagService] Getting tags on /default-domain/UserWorkspaces/admin848/Favorites failed since NXTag is missing on Favorites document type. This operation will be ignored.
  2018-12-07T16:06:40,067 WARN  [http-nio-0.0.0.0-8080-exec-11] [org.nuxeo.ecm.user.center.profile.localeProvider.UserLocaleSelectorListener] Locale Startup not available. Can't set locale
  2018-12-07T16:06:45,205 WARN  [http-nio-0.0.0.0-8080-exec-6] [org.nuxeo.ecm.platform.tag.FacetedTagService] Getting tags on /default-domain/UserWorkspaces/admin848/Favorites failed since NXTag is missing on Favorites document type. This operation will be ignored.
  

Browser-specific notes:

• In Chrome, the cursor blinks rapidly when hovering over the download button. Clicking it several times will eventually download the document – perhaps only part of the icon is clickable?
• In Edge, no amount of clicking downloaded the document.