Common matching frame work

Currently the following parts of Icecast do client and client-status matching:

<resource>
<role> (auth)
<header> (child of <http-headers>)
<event> (child of <event-bindings>)

We also expect the following new users soon:

<acl> (child of <auth>)

A common framework should be written to allow implementing matching.

This depends on #2349 (for refobject).