licenses: convert license tags to SPDX

asmrefine: update to Isabelle2019; reduce warnings

Isabelle2018: new AsmRefine session + test

Isabelle2018: new "op x" syntax; now is "(x)"

(result of "isabelle update_op -m <dir>")

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.

Removes all trailing whitespaces

Update GraphProof, slightly bitrotted.

This isn't part of any official proof at the moment, but it's a
notable next step, and I'm starting to write it up for my PhD.

CRefine: fix simp loop in Invoke_C

Also make use of prod.collapse & prod_eq_iff, dropping old versions.

Adjustments in GraphLang to support CDSL.

some of the global Isabelle2014 renames

option_case -> case_option
sum_case -> case_sum
prod_case -> case_prod
Option.set -> set_option
Option.map -> map_option
option_rel -> rel_option
list_all2_def -> list_all2_iff
map.simps -> list.map
tl.simps -> list.sel(2-3)
the.simps -> option.sel

Import release snapshot.