Make Before and After methods of *AppTest in skeleton

The test case generated by `revel new` generates methods for `AppTest`. That means that `Before()` and `After()`  receive new, independent instances of `AppTest`. This PR makes them receive `*AppTest` so you can access values of AppTest's fields After the Test that have been set Before. Note that the test itself still receives a copy of `t`, so the tests stay independent of one another.

```go

type AppTest struct {
	revel.TestSuite

	foo string        // contrived example, pretend this is a complex thing to setup
}

func (t *AppTest) Before() {
	println("Set up")
	t.foo = "bar"
}

func (t AppTest) Test1() {
	t.foo = "baz"
	t.AssertOk(t.foo == "baz")
}

func (t AppTest) Test2() {
	t.AssertOk(t.foo == "bar")
}

func (t *AppTest) After() {
	t.foo = nil
}
```