change from a synthetic compiler package to compiler_unsupported

Move from using a synthetic `compiler` package to the new `compiler_unsupported` package. This will simplify the workflow a bit, and solve one of the stumbling blocks for using pub build. Also, commit the `app/sdk/dart-sdk.bin` file. This won't be re-build by each machine, but instead versioned with the app (in addition to the compiler_unsupported and analyzer package, which both depend on it). We'll be able to rev them all in lockstep, probably ~with each dev SDK release.

@ussuri