Manage bower dependencies with grunt-bowercopy

Tracked bower dependencies are located at "src/sizzle" and "test/libs".
The source-destination mapping is in the Gruntfile.

When updating a bower dependency, update the version in bower.json, run
`grunt bower`, and then commit the result. When adding a dependency,
update the bowercopy task accordingly.

Fixes #14615.
Closes gh-1452.

Conflicts:
	bower.json
	test/index.html

test/jquery.js

@@ -32,7 +32,7 @@
 		require.config({
 			baseUrl: path,
 			paths: {
-				sizzle: path + "bower_modules/sizzle/dist/sizzle"
+				sizzle: "src/sizzle/dist/sizzle"
 			}
 		});
 		src = "src/jquery";