Updating tests using Moq to workaround Roslyn changes

https://roslyn.codeplex.com/workitem/246 affects usage of code with the
latest build of Roslyn with Moq v4.2. The workaround involves ensuring a
closure is created. Updating affected tests to make ToString() calls on
local variables to create these closures.
Remove unused `using`s from 3db0a803062df19e83bdd62b63eba47c016af384 change
- see 3db0a803062df19e83bdd62b63eba47c016af384
Introducing RazorTextWriter

RazorTextWriter represents the result of rendering a page as a sequence of
strings rather than a concatenated string. This avoids building up large
strings in memory.
Updating project.json to use frameworks token
WIP