fix: add startup workaround for trainwreck query bug

not at all clear why, but c621e21cd4b4a2a408d8a32ace0b34afe6fdf526 has
introduced some strange bug where the "first" trainwreck query will
raise an error and yet subsequent queries work fine.

so now in the startup sequence we simply force a query, which for
unknown reasons does *not* raise any error, and will somehow magically
prevent the error when a "normal" trainwreck query happens later.

AFAIK this is a "benign" operation and causes no real side effects
other than preventing the strange error. fingers crossed, this is
fine and will not cause further problems...??!

fix: cleanup old code for "record changes" session feature

had some tests failing, and one thing led to another.. apparenty we
still had support for some pretty old sqlalchemy so no need to keep
that around.

test: fix tests for `AppHandler.get_version()`

for some reason python-configuration is unreliable on certain python
versions? not sure what that's about, but this seems to work..

fix: `AppHandler.get_version()` should use upstream logic

but for now it needs a backward-compatibility wrapper

feat: move most of auth handler logic to wuttjamaican

also deprecate the `rattail.db.auth` module

fix: remove duplicate method for `AppHandler.load_object()`

that is now defined in wuttjamaican

feat: move some app model logic to wuttjamaican

previously the "canonical" way to get the model was via
config.get_model() - but now the canonical way is simply app.model

note that for now, even though wuttjamaican provides a default model,
the rattail model does not (yet?) inherit from it. also since
wuttjamaican does not yet support versioning, that feature remains in
rattail only for now.

various legacy things have been deprecated and will warn if used by
other apps.

fix: refactor code so most things work without sqlalchemy

also refactor tests to help ensure that remains true

fix: change how we override default app handler, engine maker

per upstream changes. this ensures we avoid the app handler when first
creating the engines, so that config extensions may override the
default app handler without being ignored.

Add wutta wrapper for `short_session()`

and several related tweaks for tests, docs

Incorporate the WuttJamaican package

- our AppHandler is now based on that one
- our Config *may* be based on it, if so configured

at some point our Config will "always" be based on WuttaConfig but we
need to test a bit more first

Fix broken test

now that we *do* provide a default for app_title

Add "all" product locate methods to products handler

should be able to use the handler to get exactly what you need now..

this also changes autocomplete to only fetch one product by key,
whereas previously multiple matches were *possible* - although they
were presumably not likely. guess we'll see if there is blowback

Add basic Trainwreck handler

with basic docs and tests!