feat($templateFactory): request templateURL as text/html

Added `Accept: text/html` to headers of `$http.get` invocation:

![image](https://cloud.githubusercontent.com/assets/2935356/4174128/75cddbe0-357b-11e4-9ef4-1d222813e52a.png)

Added additional unit test to `templateFactorySpec.js`:

![image](https://cloud.githubusercontent.com/assets/2935356/4174131/93906f8a-357b-11e4-9119-0e49876a7fdd.png)


This closes issue #1287