url_for needs to be app-aware

[jace]

From #230, URLs will vary between the two apps, so the url_for methods in all apps will need to be app-aware. We do this by removing the imperative url_for methods and using the declarative is_url_for decorator on views, supplying it with the app (or use ClassView with UrlForView).

Dependency: hasgeek/coaster#199

[jace]

The dependency is now resolved. There may be another dependency on hasgeek/coaster#180 if we switch to ClassView.

[jace]

The Coaster dependency is now resolved. Pending task: removing the url_for methods in all classes, switching to UrlForView in class views, and @Model.is_url_for in function views.

@iambibhas this will be part of your view rewrite.

[jace]

Resolved with #316.