Update in FragmentsRendering to names of static methods

[rstoyanchev]

FragmentsRendering#with methods have caused some confusion, making it look like adding a full template name first, and then fragment names through the builder. However, we are collecting a uniform list of fragments each consisting of a view (name) and optional model.

We should use fragment and fragments for the method names instead to be more clear:

FragmentsRendering
        .fragment("todos :: foo")
        .fragment("todos :: bar")
        .build();