Move Ferret engine "title:..." field definitions to the engine itself
Summary: Ref T12819. Move these out of the core engine into the Ferret engine. In the future different applications can define different functions, like "summary:..." or whatever. This may get more formalization when I possibly do "author:" and such some time down the road.
Test Plan: Searched for "title:...". Searched for "dog:...", got a useful error.
Reviewed By: chad
Maniphest Tasks: T12819
Differential Revision: https://secure.phabricator.com/D18536