added support for injecting guice injector and if exists then uses it to...

This enables initialize guice injector earlier and the provide it to resteasybootstrap

Example usage:

```java
//create Guice injector
Injector injector = Guice.createInjector(new ModuleImpl());
...
//create bootstrap listener instance by injector
servletHandler.addEventListener(injector.getInstance(GuiceResteasyBootstrapServletContextListener.class));
```