Create a way to keep customisations

Problem/Motivation

The Import operation is a one-click import-all action. Just as with synchronizing configuration between different environments in core it is nice to update the distribution in one swift action. However, this may include some changes that a site administrator might not like, and we should give the option to turn off specific changes to allow importing/updating the rest.

Proposed resolution

Add a module modelled after Config Ignore that resets configuration via a high-weight filter.

Remaining tasks

code
commit
test

User interface changes

new module adding new buttons to the import form.

API changes

At first just form alters.

Data model changes

New configuration for ignored config.