remove response caching

Turn out, that caching on the client side does not play well when new
data is loaded into the system.

pdb-ui/src/main/resources/application.properties

@@ -4,6 +4,4 @@ db.base=${base.dir}/db
 path.tmp=${base.dir}/tmp
 path.output=${base.dir}/out
 
-cache.images.duration.seconds=3600
-
 logging.config=classpath:log4j2.xml