Spring Framework 4.2 introduces improved support for CORS. Notably this
means that a DispatcherServlet will now process an OPTIONS request if
it contains an Origin header, without having to enable OPTIONS request
dispatching for every endpoint.

This commit takes advantage of these changes in Spring Framework 4.2 by
configuring the controller that wraps Jolokia’s AgentServlet to handle
OPTIONS requests. This allows Jolokia’s CORS support to be configured
using Jolokia’s standard configuration, as described in section 4.1.5
of the Jolokia documentation [1].

Closes gh-1987

[1] https://jolokia.org/reference/html/security.html