Deprecate list module specification in dlint.tree.kwarg_attribute

[mschwager]

Similar to #20, we should update deprecate kwarg_attribute taking a list module specification and instead take a module path.

tree.kwarg_attribute(call, "kwarg_name", ["mod1", "mod2", "attr"])

Becomes:

tree.kwarg_attribute(call, "kwarg_name", "mod1.mod2.attr")

We should also utilize the Namespace to require fully formed module paths, whereas we currently guess based on common import methods (e.g. ["OneLogin_Saml2_Constants", "DSA_SHA1"] is not the fully formed OneLogin module path).