licenses: convert license tags to SPDX

lib: Add stray lemmas and methods.

These were unused items in ARM CRefine, now kept for potential future
usefulness.

globally use session-qualified imports; add Lib session

Session-qualified imports will be required for Isabelle2018 and help clarify
the structure of sessions in the build tree.

This commit mainly adds a new set of sessions for lib/, including a Lib
session that includes most theories in lib/ and a few separate sessions for
parts that have dependencies beyond CParser or are separate AFP sessions.
The group "lib" collects all lib/ sessions.

As a consequence, other theories should use lib/ theories by session name,
not by path, which in turns means spec and proof sessions should also refer
to each other by session name, not path, to avoid duplicate theory errors in
theory merges later.

Lib: Addition of auxiliary lemmas in basic theories to better support CRefine

* Generalized version of bind_inv_inv_comm for easier swapping inside
the nondet monad

* New ccorres_symb_exec_r_known_rv

* New zip_take lemmas for handling `take n (zip x y)` situations

tags: [VER-623][SELFOUR-413]

fewer warnings

Import release snapshot.