Generate DaggerFoo rather than Dagger_Foo for generated implementations

[cgruber]

We are normalizing on a practice of using _ only in names of implementation details (e.g. AutoFactory_Blah). But since in Dagger we expect client code to directly invoke component implementations to get their builders, and to directly act on the builders, they shouldn't be dealing with Foo_Bar_Blah classes.

So for... @Component interface Foo { ... } we will generate DaggerFoo.

[cgruber]

Implemented in #145