enables AngularJS to use any jQuery, implementing issue #608

Enables AngularJS to use any jQuery library by using the `window.angularjsUseJquery` variable, that can have the following values:
  * `undefined` / `null` / `false` - the default behavior (try to use window.jQuery, if not, use internal)
  * `"internal"` - use the internal jQuery lite, no matter which other jQuery is present in the page
  * reference to any variable containing a jQuery instance

Also updated the documentation (manual bootstrapping guide) to include details about this feature.