Add the exceptions and helpers.

tui_rsync/core/shared_kernel/ports/Exceptions/__init__.py

@@ -0,0 +1,4 @@
+from .app_exception import AppException
+from .command_exception import CommandException
+
+__all__ = ['AppException', 'CommandException']

tui_rsync/core/shared_kernel/ports/Exceptions/app_exception.py

@@ -0,0 +1,3 @@
+
+class AppException(Exception):
+    pass

tui_rsync/core/shared_kernel/ports/Exceptions/command_exception.py

@@ -0,0 +1,6 @@
+from . import AppException
+
+
+class CommandException(AppException):
+    """Command failed to change persistence data."""
+    pass