Add /api/config endpoint to show the running configuration of the TSD

Signed-off-by: Chris Larsen <clarsen@euphoriaaudio.com>
Add "tsd.http.request.cors_domains" config parameter for CORS requests,
defaults to an empty string that disables CORS behavior.
Add CORS processing to RpcHandler. On creation, the class will parse the
CORS domain list from the config. Once loaded, when a request comes in with
an "Origin" header or using the "Options" method, the given domain will be
compared against the list and if matched, the proper header appended to the
response. If the domain does not match, a 200 response with an error message
will be returned immediately. See http://www.w3.org/TR/cors/
This isn't a complete, full featured implementation. It only handles the most
common tasks required by CORS.

Signed-off-by: Chris Larsen <clarsen@euphoriaaudio.com>