feat: add the import-versions command, handler logic

only works if wutta-continuum is already installed and enabled.

this also rearranges some existing classes, for better consistency

tests/cli/test_import_versions.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8; -*-
+
+from unittest import TestCase
+from unittest.mock import MagicMock, patch
+
+from wuttasync.cli import import_versions as mod, ImportCommandHandler
+
+
+class TestImportCsv(TestCase):
+
+    def test_basic(self):
+        params = {
+            "models": [],
+            "create": True,
+            "update": True,
+            "delete": False,
+            "dry_run": True,
+        }
+        ctx = MagicMock(params=params)
+        with patch.object(ImportCommandHandler, "run") as run:
+            mod.import_versions(ctx)
+            run.assert_called_once_with(params)