Fix javascript example

[jokester]

1. Follow upstream THREE.Loader to use ES class (this should fix Unable to run the example application  #737 )
2. set decoder path to load draco assets properly (if we follow javascript/README to set up a http server, assets in REPO/javascript/name will have URL path /javascript/name

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[jokester]

The super simple fix in #737 (comment) should work too, but I think modern ES class makes it easier to read.

[tomfinegan]

Thanks you for the PR!

Unfortunately, the present plan is to remove the example from our next release. The example will be replace with a link to the three.js docs and example.

[tomfinegan]

Thanks you for the PR!

Unfortunately, the present plan is to remove the example from our next release. The example will be replace with a link to the three.js docs and example.

Actually: change of plans. We will be updating the example, but I won't be able to get to this PR right away. Thanks for your patience!

[tomfinegan]

@jokester When you have the time, can you rebase and push an updated patch? Thanks!

[jokester]

@tomfinegan Sure. Just rebased my commits to latest master. The fix should still work.