Add RatpackMainApplicationUnderTest for testing apps providing a HandlerFactory.

Closes #236.
Some test simplifications.
Don't need this extra repository.
Unneeded ivar.
Remove network config.

Rely on OS tuning instead.
Move test.
Allow the Context and Background to be injected into “services” (closes #240).
Preliminary RxJava integration (#241).
Fix site tests.
Use the Rx support for the site.
Remove the registry caching for now.
Javadoc for the Rx support (#241).
Add missing annotation.
Javadoc fix.
Don't require content type to be passed to send file.

Content type can be set by using contentType() before calling sendFile.
Javadoc.
Enforce that any excludes are maven compatible and therefore expressed in POMs.
Javadoc.
Respect charset of file uploads (fixes #242).
Unused.