JS: add a freelist for the Event structure
JS: add a freelist for the Event structure

These object, like the EventNodes, can be allocated and destroyed at a very high
rate, introduce a freelist to allocated from.

Signed-off-by: Harvey Harrison <eadbd6b462bf3c97df0300a934c12bc2e5d1fe51@ausenco.com>

jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim