`ci` in this context means "Case Insensitive".
`cs` in this context means "Case Sensitive".

New models created:
    - OfficialProvider
      This was required to write a test for checking that
      OfficialProviders behaves as we expect, which was the starter
      for the original aurblup bug.

New tests created:
    - test_official_provider

Modified tests:
    - test_package_base: add ci test
    - test_package: add ci test
    - test_session: add cs test
    - test_ssh_pub_key: add cs test
Signed-off-by: Kevin Morris <kevr@0cost.org>

First off: This commit changes the default development database
backend to mysql. sqlite, however, is still completely supported
with the caveat that a user must now modify config.dev to use
the sqlite backend.

While looking into this, it was discovered that our SQLAlchemy
backend for mysql (mysql-connector) completely broke model
attributes when we switched to utf8mb4_bin (binary) -- it does
not correct the correct conversion to and from binary utf8mb4.

The new, replacement dependency mysqlclient does. mysqlclient
is also recommended in SQLAlchemy documentation as the "best"
one available.

The mysqlclient backend uses a different exception flow then
sqlite, and so tests expecting IntegrityError has to be modified
to expect OperationalError from sqlalchemy.exc.

So, for each model that we define, check keys that can't be
NULL and raise sqlalchemy.exc.IntegrityError if we have to.
This way we keep our exceptions uniform.
Signed-off-by: Kevin Morris <kevr@0cost.org>

Some of these tests were written before some of our convenient
tooling existed. Additionally, some of the tests were not
cooperating with PEP-8 guidelines or isorted.

This commit does the following:
    - Replaces all calls to make_(user|session) with
      aurweb.db.create(Model, ...).
    - Replace calls to session.add(...) + session.commit() with
      aurweb.db.create.
    - Removes the majority of calls to (session|aurweb.db).delete(...).
    - Replaces session.query calls with aurweb.db.query.
    - Initializes all mutable globals in pytest fixture setup().
    - Makes mutable global declarations more concise:
      `var1, var2 = None, None` -> `var1 = var2 = None`
    - Defines a warning exclusion for test/test_ssh_pub_key.py.
    - Removes the aurweb.testing.models module.
    - Removes some useless pytest.fixture yielding.

As of this commit, developers should use the following guidelines
when writing tests:
    - Always use aurweb.db.(create|delete|query) for database
      operations, where possible.
    - Always define mutable globals in the style: `var1 = var2 = None`.
    - `yield` the most dependent model in pytest setup fixture **iff**
      you must delete records after test runs to maintain database
      integrity. Example: test/test_account_type.py.

This all makes the test code look and behave much cleaner.
Previously, aurweb.testing.setup_test_db was buggy and leaving
objects around in SQLAlchemy's IdentityMap.
Signed-off-by: Kevin Morris <kevr@0cost.org>

+ Added aurweb.util module.
    - Added make_random_string function.
+ Added aurweb.db.make_random_value function.
    - Takes a model and a column and introspects them to figure out the
      proper column length to create a random string for; then creates
      a unique string for that column.
Signed-off-by: Kevin Morris <kevr@0cost.org>