Set up alembic migration usage (#954)

* Set up alembic migration usage

* Fix import order, add isort as alembic hook

* Only run migrations if needed

* Include date as part of migration file name for better sorting

* Skip initial migrations if tables already exist
This eases the transition from a pre-alembic state

* Fix deprecation warning in alembic revision

* Add alembic test stubs

alembic.ini

@@ -0,0 +1,72 @@
+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+script_location = alembic
+
+# template used to generate migration files
+file_template = %%(year)d-%%(month).2d-%%(day).2d-%%(hour).2d:%%(minute).2d:%%(second).2d_%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.
+prepend_sys_path = .
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the python-dateutil library that can be
+# installed by adding `alembic[tz]` to the pip requirements
+# string value is passed to dateutil.tz.gettz()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the
+# "slug" field
+# truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; This defaults
+# to alembic/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "version_path_separator"
+# version_locations = %(here)s/bar:%(here)s/bat:alembic/versions
+
+# version path separator; As mentioned above, this is the character used to split
+# version_locations. Valid values are:
+#
+# version_path_separator = :
+# version_path_separator = ;
+# version_path_separator = space
+version_path_separator = os  # default: use os.pathsep
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+# Will be replaced in alembic/env.py with the actual url
+sqlalchemy.url =
+
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+hooks = isort, black
+
+# format using "isort" - use the console_scripts runner, against the "isort" entrypoint
+isort.type = console_scripts
+isort.entrypoint = isort
+isort.options = REVISION_SCRIPT_FILENAME
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+black.type = console_scripts
+black.entrypoint = black
+black.options = REVISION_SCRIPT_FILENAME