Rule: Do not extend Block from deprecated parents

[jissereitsma]

A rule should check whether a Block is extending upon Magento\Backend\Block\Widget\Form\Generic and Magento\Backend\Block\Widget\Grid\Container (and possibly others) which are deprecated. The rule should respond that a UiComponent should be created instead.

Rule

The classes Magento\Backend\Block\Widget\Form\Generic and Magento\Backend\Block\Widget\Grid\Container are deprecated since Magento_Backend version 100.2.0 (so more or less Magento 2.2). Instead, UiComponents should be used.

Reason

Only with UiComponent, other people can easily add custom uiComponent XML to extend upon the original form. Even though creating UiComponents might be hard, using them brings more flexibility than the deprecated Block parents do.

Implementation

This is implemented via #51

[jissereitsma]

This needs to be added to a ruleset.xml specific to Magento 2.2.