all: remove theory import path references

In Isabelle2020, when isabelle jedit is started without a session
context, e.g. `isabelle jedit -l ASpec`, theory imports with path
references cause the isabelle process to hang.

Since sessions now declare directories, Isabelle can find those files
without path reference and we therefore remove all such path references
from import statements. With this, `jedit` and `build` should work with
and without explicit session context as before.

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

licenses: convert license tags to SPDX

global: isabelle update_cartouches

lib: option (reader) monad syntax and gets_map operator

lib: prettier monad type printing

Removes all trailing whitespaces

lib: new invariant syntax "f {|P|}"

Precedence chosen between bind and equality such that
f >>= g {P} = foo {Q} works as expected.

Isabelle2016-1: fix some proofs broken by abs_def normalisation

Unfolding now automatically converts definitional rules to abs_def
normal form before rewriting.

lib: start disentangling spaghetti word dependencies