Add manifest file for Firefox OS

The built version of sampler can run on FxOS if we provide
a manifest.webapp file in the root. This is a basic one
based on the documentation samples.

Enyo-DCO-1.1-Signed-Off-By: Ben Combee (ben.combee@lge.com)
Merge pull request #54 from enyojs/add-fxos-manifest

Add manifest file for Firefox OS