Bug 951 - Externalize cors definition of restconf

Create new project called filter-valve that allows defining filters
outside of web.xml. An xml file is added to configuration folder
of distribution.

The valve allows any kind of filters to be applied around each
request, mapping contexts and path pattern same way as servlet
specification does. The xml file allows defining filter templates,
each context (WAB) can reuse and modify the common configuration.

Currently only restconf has externalized cors filter definition.

Change-Id: Ia8b6053efdff2b3c1150eec95e63b460d84c457e
Signed-off-by: Tomas Olvecky <tolvecky@cisco.com>