Break out the half of business_logic.py into models.py

This breaks out the Workspace, ReleaseRequest, and CodeRepo classes (and
their dependant sub-objects) into a new models.py file.

This is just moving code around and changing imports, there's no actualy
code changes. It also splits half the even larger test_business_logic.py
file into a test_models.py file to match.

This and the preceding changes takes the currently 2200 line
business_logic.py file down to 1198, with models.py clocking in at 896.
Likewise, the test_business_logic.py is currently at 4008 lines, but
this change splits it into two files, 2935 and 797 respectively.

There may be futher changes and cleanups possilbe here - this commit
limits itself to mechanical changes to split files.

airlock/file_browser_api.py

@@ -7,14 +7,13 @@
 from typing import Protocol
 
 from airlock import renderers
-from airlock.business_logic import (
-    ROOT_PATH,
+from airlock.enums import PathType, RequestFileType, WorkspaceFileStatus
+from airlock.models import (
     CodeRepo,
     ReleaseRequest,
     Workspace,
 )
-from airlock.enums import PathType, RequestFileType, WorkspaceFileStatus
-from airlock.types import FileMetadata, UrlPath
+from airlock.types import ROOT_PATH, FileMetadata, UrlPath
 from airlock.users import User
 from airlock.utils import is_valid_file_type
 from airlock.visibility import RequestFileStatus

airlock/forms.py

@@ -1,8 +1,8 @@
 from django import forms
 from django.forms.formsets import BaseFormSet, formset_factory
 
-from airlock.business_logic import FileGroup
 from airlock.enums import RequestFileType, Visibility
+from airlock.models import FileGroup
 
 
 class ListField(forms.Field):