Move patch script class to the server tree.

The PatchScriptFactory and PatchScriptBuilder were previously in the
httpd tree. Move them to the server tree so the implementation of the
revision diff REST API can share the logic.  Also, update
PatchScriptFactory to implement Callable instead of Handler, so
there is not a circular dependency.

Change-Id: Ic20fbf81a2da5ad5e2fd5c3542e6caa47df33cea
5 files changed