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.

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

Move tests out of the installed package set

this seems to be better practice. from what i can tell this is a
clean move with no breakage.. and built package files no longer seem
to include test modules

Make 'tests' a proper subpackage again; add some tests

Trying to make more of an effort here...

Fix a few tests, comment out a bunch also.

Wow the tests are really showing their lack of love...

General header / Unicode cleanup.

This hopefully updates all module headers such that the file encoding is
utf-8, and uses Unicode literals, etc.

Add support for older SQLAlchemy (0.6.3 specifically).

It's possible this still misses some things, but at least tests pass...

Add "deletable orphan" awareness when recording changes.

Turns out there was a long-standing bug where orphans which were deleted
from the host would be marked as "changed" (instead of deleted), causing
the store databases to keep the orphan.

Refactored model imports, etc.

This is in preparation for using database models only from `rattail` (i.e. no
`edbob`). Mostly the model and enum imports were affected.