Add frontend/backend make targets, fix source release (#10325)

* Add frontend/backend make targets, fix source release

- Add 'make backend' and 'make frontend' make targets which are used to
  build go and js/css/svg files respectively.

- The 'backend' target can be invoked without requiring Node.js to be
  present on the system if pre-built frontend assets are present like
  in the release source tarballs.

- Fix source releases missing 'dist' folders inside 'node_modules' which
  were erronously excluded from tar.

- Store VERSION in file VERSION for the release tarballs and prefer that
  file over git-derived version.

* fix release task

* fix typo

* fix another typo

.gitignore

@@ -74,6 +74,7 @@ coverage.all
 /public/css
 /public/fomantic
 /public/img/svg
+/VERSION
 
 # Snapcraft
 snap/.snapcraft/