Add a field to hold "project type" (sandbox, full, n/a) info

We need a way to know if a given node (type) is a project node type. D7 OG works by providing a field that you can attach to any node type which controls how nodes of that type interact with OG (be a group, be a group post, ignore). I think we can do something very similar here by having a field that records the project type (I know this terminology is overloaded) -- is it a full project, a sandbox, or not a project at all. That way, you can add this field to any node types you want (e.g. on d.o, we'd have different node types for modules, themes, etc) but we could still do things like "show me all the project nodes owned by user foo" without hard-coding node types. And, it gives us an obvious way to handle the whole sandbox vs. full project stuff (which is now just a custom column in the {project_projects} table).