Web Admin - Preset Warning Messages

[Bluestrings-Drawpile]

From #914 ... Moderation, 9 Priority: Medium to High

Ability to pre-save messages with short description (web admin, remote admin) about rules being broken to auto send to session in question quickly, and these messages are saved server side so they're accessible from web admin for other moderators.

Problem: I end up sending a lot of repeat messages, like session name is inappropriate. Having some pre-saved messages would be handy (e.g. session name needs to be SFW, session name should be changed or marked NSFW, session should be marked NSFW, etc).