Build a minified version of vaadinPush.js in vaadin-push.jar (#11630)

* Replaced jquery and jquery.atmosphere.js with original, unmodified versions
* Added vaadinPush.js build target to ide.xml and push/build.xml
* Uses yuicompressor to compress the resulting push javascript

Change-Id: I59ba9c2bbf74e05d10325d38efdb106b638cd8e7