Splitting externals


The  `buildout` _ol3-serverconfig_ is run on all server, even when deploying. It generate two build environment dependent files  `serverconfig.js`and `layersconfig.<lang>.js`

The parts `ol3-update`is run only at will.

If anybody knows how to correctly escape the content of `layersconfig.<lang>.js` into the loader's `<scri' + 'ipt>`tag, I would be happy