Coffee restructuring

Add a list of feature to COFFEE and PyOP2, including:
- Compilation with the Intel compiler
- AST nodes are now printable just by typing "print node"
Also:
- The name "coffee" takes the place of "ir"
- Some classes, methods, and variables in COFFEE are renamed to better reflect their semantics
- The COFFEE initializer is moved from ast_vectorizer to ast_plan, where it should stay: we actually initialize COFFEE, not just its vectorizer

To reflect the change from "ir" to "coffee", Firedrake and FFC are modified as well - dangling pull requests are waiting for your approval.