Upgrade Peewee to latest 3.x

This requires a number of small changes in the data model code, as well as additional testing.

data/model/test/test_basequery.py

@@ -1,6 +1,6 @@
 import pytest
 
-from peewee import JOIN_LEFT_OUTER
+from peewee import JOIN
 from playhouse.test_utils import assert_query_count
 
 from data.database import Repository, RepositoryPermission, TeamMember, Namespace
@@ -87,7 +87,7 @@ def test_filter_repositories(username, include_public, filter_to_namespace, repo
            .distinct()
            .join(Namespace, on=(Repository.namespace_user == Namespace.id))
            .switch(Repository)
-           .join(RepositoryPermission, JOIN_LEFT_OUTER))
+           .join(RepositoryPermission, JOIN.LEFT_OUTER))
 
   with assert_query_count(1):
     found = list(filter_to_repos_for_user(query, user.id,

data/model/test/test_repository.py

@@ -8,6 +8,7 @@ from data.model.repository import create_repository, purge_repository, is_empty
 from data.model.repository import get_filtered_matching_repositories
 from test.fixtures import *
 
+
 def test_duplicate_repository_different_kinds(initialized_db):
   # Create an image repo.
   create_repository('devtable', 'somenewrepo', None, repo_kind='image')