Set a useful avatar for the bot

[pmonks]

Avatars are a powerful visual cue for Symphony users to clearly identify the bot from amongst a set of other Symphony users. The bot should, therefore, set a visually distinctive avatar image for itself.

[pmonks]

Currently it is not possible for a bot to set its own avatar image due to an entitlement checking bug in Symphony's user management API (the insecure workaround is to grant the bot the user administration entitlement, which then lets it manipulate any user profile in the pod - a security hole that makes this workaround unacceptable).