1. Allow player to specify custom art for the personal assistant.

2. Rework PA art rendering, so it's all done directly via DOM.
3. Allow `App.Events.drawEventArt` to automatically render the personal assistant when requested.
4. Replace `App.Art.refreshSlaveArt` with the higher-level `App.Events.refreshEventArt`, since it's only ever used for event art anyway (and support assistant art too).