Plugin2: Animation Panel has Java 6 dependency

The new plugin supports runngin java applets in 1.4.2 and 1.5 JVM. Deploy and plugin code on client vm side need be compatible with as low as 1.4.2. The current animation panel is using some jre 6 feature. It throw ClassNotFound, for example, java.awt.RadialGradientPaint.class, when run in 1.5.x jvm.

To support multiple JREs, Animation Panel need take jre runtime version into consideration.