modernize js and use babel (#8973)

* modernize js and use babel

- add babel toolchain to transform modern JS to ES5
- extend eslint config for modern rules
- fixes linting issues via `eslint --fix` and manual fixes

* run 'make css' to satisfy CI

* code style tweaks and set js indendation to 2 in .editorconfig

* regenerate js

.editorconfig

@@ -24,7 +24,7 @@ indent_size = 2
 
 [*.js]
 indent_style = space
-indent_size = 4
+indent_size = 2
 
 [Makefile]
 indent_style = tab