feat: changes screen implementation (#117)

Add support of changes generation. Changes will be generated (unless explicitly asked not to) automatically during check process (i.e. `repo-update --dry-run` and aliases) and uploaded to the remote server. Changes can be reviewed either by web interface or by special subcommands.

Changes will be automatically cleared during next successful build

docs/ahriman.application.handlers.rst

@@ -20,6 +20,14 @@ ahriman.application.handlers.backup module
    :no-undoc-members:
    :show-inheritance:
 
+ahriman.application.handlers.change module
+------------------------------------------
+
+.. automodule:: ahriman.application.handlers.change
+   :members:
+   :no-undoc-members:
+   :show-inheritance:
+
 ahriman.application.handlers.clean module
 -----------------------------------------