Rename ServletHandlerFactory -> HandlerFactory

Includes rename of implementations:

  * `AbstractServletHandlerFactory` -> `AbstractHandlerFactory`
  * `DefaultServletHandlerFactory` -> `DefaultHandlerFactory`
  * `ContextServletHandlerFactory` -> `ContextHandlerFactory`
Use ImmutableList for Handler Connectors.
Rename ServletHandlerFactoryTests
Fix incorrect ordering of fields/accessors

The `gzip` field was incorrectly placed in `AbstractHandlerFactory`.
Provide initializers for ContextHandlerFactory

Instead of a unary String constructor, we should use these static
initializers, as the constructor confuses Jackson.
Add test for ContextHandlerFactory