Fix addApp returning a promise in the middle of the promise chain (hid error messages)
Fix ServeInstaller NPE by having installPath accessed as a property always
Fix "updating" message being cleared only on success.
Use URLs everywhere instead of paths. Removes need for "root" filesystem

This also removes CRX file special-casing in launch logic by:
1. Installing CRX resources into a "www" subdir (like Serve does)
2. Taking advantage of the new allowFurtherRemapping setting for aliases
UrlRemap: Use a nicer name for the "ignore-me" request header.