Serve static resources for non-jar Server plugins

Abstract from the Server plugins external packaging
and allows to serve static resources from any
form of Server plugin that exposes a PluginContentScanner.

This allows potentially other forms of plugins
(e.g. Scripting, directory-based or any other) to
provide their on-line documentation and serve their
static resources.

Change-Id: I80b8159cf87255e3132298f5863b374b5bd44a6c
3 files changed