Implement a persistent cache for computed dependency data (classpath)

[plaird]

I was in the middle of a refactor when I had to restart my machine. When I brought Eclipse back up, the classpath could not be computed because there were build errors. Also, for performance reasons, it is sad to redo all the work to compute the concrete classpaths (with actual paths to jar files) on restart of an IDE.

The SDK should have the option to persist a materialized copy of the classpath (e.g. see .classpath from m2eclipse).