warn about unimplemented methods

This changeset adds logging of the various native and non-native methods that we've stubbed out, to make them more noticeable and help us track down bugs and issues caused by unimplemented methods. The natives all use console.warn to log to the web console. The non-natives either throw an exception or log to the in-page log using System.out.println.

There are some methods whose status is unclear, so I might have missed some stubs (or added logging in stubs that are actually implemented). @marco-c and @fzzzy: can you take a look at this as well?