Rules : add a rules section and a way to edit them

[vincent-peugnet]

The simplest way could be a markdown file stored in the app files.
But only one admin could edit it.
It could be interesting to add the ability to allow moderators edit the rules.

AND

The most complex but interesting strategy could be to use a git-like rule system, but using a vote system to validate rules or not.
Voters could be mods of course, but also some users as defined by user-classes.

This could as well be done by some external dedicated tools, with a SAML connection #40 🥺 But I doubt on this solution.

Actually vote system for rules are very related to important aspects of this project. This would be a great implementation but maybe not too soon as it need a lot of work to do it well.

[vincent-peugnet]

As writen in #46, a rule could be an entity in the database. That way it could be cited in warnings. This could be a simple way to do this at first.

A rule classwould be defined by:

• an ID
• name
• text (in markdown ? not so shure.. )
• createdAt
• lastEdiAt

The question is: should rules have the ability of being edited ?
Or should they only be "forked". Do we need a historic of this ? It's clearly more complicated.
I like the idea of an ID will be for ever linked to one written rule.