mimosa watch + module config, cannot update on the fly

[dbashford]

You cannot run mimosa watch and have mimosa run and re-run modules based r.js runs.

One reason is because of source maps. The initial build has no issues, source maps work, but the next build after starting mimosa watch will have issues because of all the source map artifacts in place after the first build. So, need to, by default, disable source maps for modules runs, but allow via require.optimize.overrides to force source maps for those that need it for a single run.

Another reason is because the original module files get written over during the build with the optimized files. So need to cache the originals and slide them in before restarting a build

[dbashford]

From dbashford/mimosa#297

[dbashford]

This commit did most of the work: c37e2e0