Feature summary (what you would like to be able to do and where):
Add an option to allow users to always enable safemode.
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
This can be useful when:
- Users don't trust interface administrators (of a wiki on a wiki farm, etc.).
Benefits (why should this be implemented?):
Users will not need to type ?safemode=1 multiple times when browsing.
Downstream task: https://phabricator.miraheze.org/T10368