Allow a standalone JS viewer (without requiring Web2py)

[hyanwong]

For people who want to develop the JS code, we should really not require them to run an entire web2py server. There should be a way to call the JS code from a static web page, and get nearly everything else, API calls, etc, (although perhaps not the completetree etc. files?) from our server. This should mostly be easy, as we can specify which URLs to use for the API etc in the treeLayout page.

In fact, I think the main issue here is internationalisation, because we load up the UI from a served-up web page (viewer_UI.load) which is translated into different languages. However, we could simply ask the downloader to pick a particular language, and save a copy of viewer_UI.load in that language.

[hyanwong]

Now mostly done, will require some bug fixes, e.g. for popular species