Add --no-output

This is at least a partial resolution for https://github.com/google/closure-compiler/issues/478.

Specifying the `--no-output` command line parameter skips output and runs only checks.
It works in with each of the compilation levels.

There was an existing `skipNormalOutputs` in `CommandLineConfig` that almost worked, except it skipped checks. (It is meant for outputting dependency info, etc.)