Make the j2kDecodeCache expire after 50 minutes (configurable). Alse allows

setting the path for it. This commit introduces NEW DEFAULT BEHAVIOR. To
retain the old behavior (eternal cache) you will need to change your OpenSim.ini
and set the timeout to 0.

bin/OpenSim.ini.example

@@ -1366,6 +1366,13 @@
     ;
     ;TextureDataLimit = 5
 
+;; The JPEG2000 decode cache
+;; Timeout is in minutes
+
+[J2KDecoder]
+;CacheDir = "./j2kDecodeCache"
+;CacheTimeout = 60
+
 ;;
 ;; These are defaults that are overwritten below in [Architecture].
 ;; These defaults allow OpenSim to work out of the box with