Release rollbackable (config- and settings-) destination plugins

Problem/Motivation

There are some migrate destination plugins in Drupal core which aren't rollbackable. Since we needed this feature, we wrote our own plugins which can replace the corresponding core-provided ones.

In the hope that others may benefit from using these plugins, we would like to publish them.

Proposed resolution

• Create a MigMag submodule migmag_rollbackable for holding the plugins and their tests.
• Create a MigMag submodule migmag_rollbackable_replacefor replacing the non-rollbackable plugins with their corresponding rollbackable variants.

Remaining tasks

Create the patch.

API changes