* Porting Hidden and HiddenFor unit tests

Partial fix to #453
need to test a few additional expressions
- identity expression (mentioned below) i.e. `m => m`
- deeper property paths e.g. `m => m.Property1.Property2`
- list and dictionary indexing (whatever will work w/ current model binding) e.g. `m => m.Property["key"]`, `m => m.Property[indexVariable]`, `m => m["key"]`
- simple variable references e.g. equivalent of
``` c#
  var value = Model[index].Property1.ToString();
  @Html.HiddenFor(m => value)
```
- ...