Allow timeout customization of DefaultHTTPClient

[intabulas]

DefaultHTTPClient (when using the cli vs as a lib) has hard wired timeouts. Some of the sites I want to test are data intensive reporting apps that well exceed the (as an example) the 5 second response header timeout. My solution was to use checkup as a lib in my own cli app with a customer client for HTTPChecker

It would be nice to have options in a checkup.json to override those default timeouts so one does not have to use it as a library to meet their needs