Fix manifest so app will load in Chrome
Update package file so it's in line with crx manifest
Update grunt config to enable build for both crx and wgt

Also updated package task so it's a multitask, to enable
multiple package types (e.g. in this case .wgt)
to be built from a single grunt config.

For the crx build, grunt crx will copy all of the required
files to build/crx. However, I don't currently have a grunt
task to produce valid crx packages, so you have to load
the build/crx folder as a Chrome developer extension to see it
working.
Fix Makefile for local install