add revisioning task to gulp build

* 'public' directory is now removed on gulp build
* Copies built .css and .js files to <filename>-<hash>.<extension>
* Replaces references from built .html files to match the revisioned files
* Keeps the original built files intact, but this is most likely going to change in the future

.gitignore

@@ -3,3 +3,4 @@ node_modules
 bower_components
 public
 .DS_Store
+rev-manifest.json