to occur in the background without interrupting gameplay.

* Added a game options setting to allow use of different generation
steps for temporary images.  Personally, I use 30 steps for temporary
images and 300 for persistent images.

* Temporary render requests are added to the beginning of the queue and
use PassageSwitchHandler to cancel and remove the request if the player
moves to another passage before rendering is completed.

* Added an option to automatically regenerate images at regular intervals.

* Added "float: inline-start" to report images to prevent them cascading
oddly when the report descriptions are short.

* Added regular cleaning of the imageDB to discard images that no longer
have attribution.

* Added a button for issuing the Interrupt command to SD and clearing
the generation queue.