Change Metasploit::Model::Spec::Template.root to class variable

MSP-9228

Needs to be class variable so that setting
Metasploit::Model::Spec::Template.root will also affect subclasses like
Metasploit::Model::Module::Ancestor::Spec::Template.root.
Move Templates under app/models

MSP-9228

The Metasploit::Model::Module::*::Spec::Templates are models, but I
had put them under lib by mistake.