Move lambda type, dest_term function to kernel; add identical fn

dest_term is quite heavily used (it implements SML's best
approximation of a "view" for pattern-matching against terms), and its
implementation outside the kernel is needlessly inefficient.

Also extend signature with identical function, which correctly says
whether or not two terms are identical, including in their choice of
bound names. In the standard kernel, the possible presence of
explicit substitution terms means that this notion is not the same as
simple equality on terms.

More theory signature events now reported to hooks.

In particular, {new,remove}{typeOp,constant} events are reported.

Use this to do away with some of the cruftiness in boolLib whereby the
entry-points there had to mask the primitive principles in order to
update the grammar. Now the parser installs hooks to watch for things
being deleted or added and adjusts the grammar as it goes.

The disadvantage is that it's impossible to bypass these changes to
the grammar.

Rename TruePrefix to Prefix; use fixity options with NONE for what was Prefix.

90+% of this work was done by Ramana Kumar. The following list are
the commits for a series of individual commits that have been squished
into one big change:
* remove mention of TruePrefix from the add_rule docfile
* first batch of changes removing TruePrefix from src/parse
* replace TruePrefix by Prefix in boolScript.sml
* remove TruePrefix from Rsyntax
is a fixity ever required for new_specification?
* some more Prefix -> NONE and TruePrefix -> Prefix in theories
* TruePrefix changes for datatype
* TruePrefix changes for res_quan
* TruePrefix->Prefix in a TeX selftest
* TruePrefix changes for quotient
* TruePrefix changes for integer and real
* fix quotient examples for TruePrefix removal
* more fixes for quotient examples
* fixes for lambda example for TruePrefix removal
* Reword description manual in light of removal of TruePrefix.
* Fix msgTheory quotient example; Poly 5.3 had problems with monotypes.
* Fixes for files in examples/lambda given removal of TruePrefix.
* Fix in examples/unification given removal of TruePrefix.
* Fix in examples/HolCheck given removal of TruePrefix.
* Fixes in examples/acl2 given removal of TruePrefix.

Change src/bool to src/1 as a prelude to experimentation!