Initial import. Partially completed Push.java

This is being saved before I fork it to try out NanoHTTPD instead.
Working HTTP server version
Fixes to Push code. Now navigating from Javascript.
Working /push. Add /exec and /menu.

- Currently only cordova serve pushes are supported:
    /push?type=serve&name=<appname>&url=<serve URL>
- Run arbitrary Javascript in the app:
    /exec?code=<JS code, be careful of HTML encoding>
- Return to the main App Harness menu:
    /menu
Adding LICENSE and README.
Markdownify the LICENSE more fully.
Now with push support for crx files
Merge harness-push plugin into this repo.