Removed redundant addsimps of Un_insert_left, which is now a default simprule

Removal of monotonicity reasoning involving "lost" and the theorem Agent_not_see_encrypted_key, which (a) is never used and (b) becomes harder to prove when Notes is available.

Now uses the Notes constructor to distinguish the Client (who has chosen M) from the Spy (who may have replayed her messages)

Moved some declarations to Message from Public and Shared

Now loads theory Event, which contains common declarations

Moving common declarations and proofs from theories "Shared" and "Public" to "Event". NB the original "Event" theory was later renamed "Shared". Addition of the Notes constructor to datatype "event".

removed obsolete init_pps and init_thy_reader;

improved type checking errors;

removed init_pps;

removed init_database;