Avoid registering static resources on registries

[hvelarde]

The revolutionary approach chosen for Plone 5 resource registries rewrite makes difficult to maintain single add-on versions that work in both Plone 4.3 and latest Plone 5:

• some of the JavaScript tools used (Bower, Grunt, RequireJS…) seem to be less attractive nowadays than more modern options (webpack)
• Resource bundling was a workaround for a limitation of the HTTP/1.1 protocol and not a CMS feature; HTTP/2 makes it unnecessary and even undesirable

Getting rid of the resource registries registrations will make upgrades much easier.

refs. plone/Products.CMFPlone#1896
refs. #819

[idgserpro]

I think #613 can be closed when this is finished.