Manage the module configuration

Problem/Motivation

Once the #2 is made, we need to manage the module configuration.

Proposed resolution

Create a Simple Configuration Form to manage the following variables:

- node_revision_delete_cron
- node_revision_delete_last_execute
- node_revision_delete_time

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.