prevent extra db connection from being created so that the original one can be re-used throughout the entire test session again
simplify: `setup_app` already is a callable
separate the database setup (`initialize_sql`) from app configuration (`base_configure`)

that way the test setup doesn't need to mock the db setup away in order to perform better
separate pytest arguments for easier (temporary) exclusion of doctests
(temporarily) disabled `test_stamp_heads` as is causes isolation issues due to creating an extra database connection (via alembic's migration scripts)

note that this exposes another test failure, which was introduced by 3403b089 (in `test_root_default`) and needs to be fixed first
separate creation of the db connection and test content

this way the workflow engine can be initialized before any content is created, in particular the root node.  with this the workaround to get a "clean" root (from f12f9d9d) or rather its update (from c494bca1) can be removed again.  this is because the only difference from the root node created in the `connection` fixture before and the "clean" one was the workflow state, in fact.

also note that a number of workflow-related tests are currently still failing...
Merge pull request #2 from witsch/get_rid_of_unittest

prevent extra db connection from being created...