add type information to RenderedTrees (Fixes #106)

use a single case class for RenderedTrees (but with alias constructors Terminal and NonTerminal)

nodeTypes for Workflow trees

nodeTypes for LogicalPlan (and annotated forms)

nodeType for None

nodeTypes for AST annotations

handle the umpteen AST node types in RenderTree instance
How would the front-end render a node without a label?