Analyzer

This adds initial integration of the analyzer into Spark. It supports parsing files into ASTs (w/ errors), without resolution. It also supports parsing simple dart source - that only imports `dart:core` - with resolution.

This does not support resolution of code that uses package:, file, or dart: imports beyond `dart:core`. That will require investigation of running the analyzer in a web worker where synchronous I/O operations are available. Alternatively, the analyzer itself will need to investigate supporting async I/O.

@dinhviethoa , @scheglov

Also, brianwilkerson@google.com, I'd also like to get your eyes on this. I don't think you github however. A review process on github is much like for the Dart repo. You can annotate lines of source with questions or comments, and comment on the CL in general.