Add chef finders module

This module represents the Chef findable role.

It unifies the query methods of Node/Role/Client/Proposal objects
and provides Rails 2-like find_(all)_by_attr1_and_attr2 interface.

The role expects chef_class and chef_type methods to be overloaded.
chef_class returns the underlying Chef model (e.g. Chef::Node),
while chef_type returns the index name, e.g. "node".

It also provides after_find_filter, which can be overrided to filter out
e.g. nil or unsuitable results from searches.
Add deprecation helper

The helper prints a warning and a caller location, so that the method
can be converted to a new syntax suggested in the message.

The hope is that people who hate deprecation warnings will gradually
convert the code.
Convert ClientObject to use new finders
Convert NodeObject to use new finders
Convert RoleObject to use new finders
Convert ProposalObjects to use new finders
Include modules in the superclass
Remove query_chef from chef object

Use the same method in finders instead