Support workspace files with spaces in their names

[cgrindel]

Currently, the rules rely on passing workspace files to the child workspace using runfiles. However, a known Bazel issue prevents files with spaces in their names from working properly. Ideally, this will be fixed in Bazel. However, for now, we may want to allow a client to specify whether to use an alternative mechanism.

Possible solutions:

1. Add the files to an archive file and pass that through runfiles
2. Create a mechanism that creates symlinks from a more robust file format as compared to the current, space-delimited format.