Better tests for the deprecated SimpleUriImageLink (and query).
Removed unused code from SimpleUriImageLinkTest.
Slightly adjusted InputStreamImageLink, so that it is now somewhat easier to test.
Added tests for InputStreamImageLink.
Added tests for UriImageIOQuery.
Background executors now clear the thread interrupted status before executing tasks or cleanup tasks.
Added the commonly used RunnableDispatcher and related static utility methods.
Removed the numerous implementations of RunnableDispatcher.
Fixed a checkstyle error.