add task_prior_func for worker so it can decide when to update priority
of neighbours
Re-organise lpel_config and implement location-based priority
 + re-organise lpel_config to contain all user-defined parameters, this
 will be passed to WorkerInit
 + location-based priority: task priority is based on the entity
 location -> this requires the comparision function from snet-rts -->
 this is specified in lpel_config
update task prior in case neg_lim is not defined
fix bug in taskqueue: priority is compared for t->inarg
change isPriorGreater -> comparePrior for more general