Move letter-avatars into own request

To prevent further weakening of our CSP policies, moving the Avatars
into a non-inline version is the way to go.

This implementation probably needs some beautification. But already fixes
the bug.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

lib/web/userRouter.js

@@ -5,6 +5,7 @@ const Router = require('express').Router
 const response = require('../response')
 const models = require('../models')
 const logger = require('../logger')
+const {generateAvatar} = require('../letter-avatars')
 
 const UserRouter = module.exports = Router()
 
@@ -34,3 +35,9 @@ UserRouter.get('/me', function (req, res) {
     })
   }
 })
+
+UserRouter.get('/user/:username/avatar.svg', function (req, res, next) {
+  res.setHeader('Content-Type', 'image/svg+xml')
+  res.setHeader('Cache-Control', 'public, max-age=86400')
+  res.send(generateAvatar(req.params.username))
+})