Always use the current working directory as the root path.

This fixes a bunch of problems with source maps. This means
that all files in the config.js file should be relative to the working
directory (and not have "./"" prefixes). Without this change, a path like
"/home/user/foo/bar/baz/../../../blah" will have names that show up in
sourcemaps as URLs that cannot possibly exist, like
"/input/myconfig/../../../blah".

Remove the caching response header change because it doesn't work. When you
refresh your browser your client is going to send cache-control: no-cache
because it was a forced reload. So the caching headers only really help if you
randomly navigate to your plovr server, not the standard dev workflow.
Update to local branch of my closure-templates dependency