Add manifests to make the app a progressive webapp. There are 2 manifests : one
during the installation process (while the app is loading) and one for the app
itself.  Note that the "start_url" parameter is made for the officejs app URL
([your_app].app.officejs.com/[release_number]). It doesn't work on an ERP5
instance ([instance_url]/erp5/web_site_module/[your_app]). If you want to make
it work on the ERP5 instance for testing purposes, remove one "../".

Update the Javascript Editor logo according to Vincent's wishes.