Update to latest ol3/ga API

This PR makes the latest ol3 (corresponding to PR https://github.com/geoadmin/ol3/pull/109) available for testing. To reach the new versions, the user has to use the `mode=preview` or `mode=previewdebug` on the loader. Default loader is still serving the old versions. Our clients can therefore check their version first before we switch it for good.

The `preview` and `previewdebug` modes have been tested with our examples and with all codepen examples. They are working well without any adaptions.

Note: once we switch it for good, we need to do what is described in #1006