Updates references to module import paths

See revel/revel#785 for more details.
@brendensoares, sorry, could we use
```Go
Config.StringDefault("module.testrunner", "github.com/revel/modules/testrunner")
```
instead of
```Go
"github.com/revel/modules/testrunner"
```
Just like as we are doing it in [revel/revel/pull/720](https://github.com/revel/revel/pull/720).

So it will be possible to use third party test runners.