Make responsive_preview a suggestion rather than a hard dependency

Problem/Motivation

responsive_preview module is added a dependency of this module, presumably for the benefit of councils which block mobile preview mode in browsers on their systems.

However, this adds overhead for sites in councils which do not impose this restriction. Also, the module is not without its problems, e.g. 🐛 Crashes on config entities that define a canonical link template Active .

Steps to reproduce

Proposed resolution

Make this a suggestion in the README rather than a hard dependency.

Remaining tasks

User interface changes

API changes

Data model changes