Add feature: override role name displayed to end user from config option

[Kirrus-Indiestone]

This patch adds a configuration option which will let end users arbitrarily override the role displayed to end users from the config option overrideRoleNameDisplay

This allows to hide a moderator with a hitched role which is unsuitable to be displayed to end users. In our case, specifically a hidden moderator with a general user role. Not able to use fallbackRoleName, because the hidden moderator has a hitched role.

I have not coded in a very long time, and never in JS before, so rusty doesn't even begin to cover it. Thoughts/rejection/comments/patches appreciated :)

I've tested this patch on our server, and it appears to work okay, but have not tested all existing functions exhaustively

[Kirrus-Indiestone]

TODO:

• Verify fallback works when override not in effect
• Document option in configuration.md

[Kirrus-Indiestone]

Fallback still works whilst override not enabled, configuration option documented