Make resources receivable from external repositories/cdn's etc

**I'm submitting a bug report**

* **Library Version:**
1.0.2

**Please tell us about your environment:**
* **Operating System:**
Windows 10

* **Node Version:**
4.6.0

* **NPM Version:**
3.10.10

* **JSPM OR Webpack AND Version**
aurelia cli

* **Browser:**
all

* **Language:**
all

**Current behavior:**
External resources (i. e. custom elements) cannot be referenced.
If I try to reference a custom element from here:

`config.globalResources(["https://www.cdn-intranet.com/resources/elements/test-stuff"]);`

it tries to resolve the url "as-is" and does not try to resolve it for ".js" and ".html". In fact, it tries to resolve `https://www.cdn-intranet.com/resources/elements/test-stuff` and received a **404**. I also tried

`config.globalResources(["//www.cdn-intranet.com/resources/elements/test-stuff"]);`

but it doesn't work, too.

**Expected/desired behavior:**
It would be neat if aurelia would not make a difference between locally or externally available resources.

* **What is the motivation / use case for changing the behavior?**
We are serving 60.000 employees across the world. Saving and optimizing bandwith is important to us. Custom elements like grids, tables, layout stuff etc. do not change and are equally implemented in all our applications. Deploying these custom elements on a loadbalanced web server ensures that browsers cache these elements across all our 400 applications. We are actually doing this with our current knockout-based framework, too, and works perfectly.