Multiple interfaces breaks navigation

_From @gkinsman on March 26, 2015 6:6_

Teapot isn't able to find implementations of interfaces when the implementation implements multiple interfaces.

```
interface IBar<T> { }
interface IBaz<T> { }
class Foo<T> : IBar<T>, IBaz<T> { }
```

Navigating from usages of IBar<T> or IBaz<T> won't find either implementation.

_Copied from original issue: DevRust/Teapot.Public#1_
