allow to use page() and count() together on a query

Queries provide a powerful interface to access JBPM tasks, jobs, deployments, etc;

currently the only way you can get the number of results that match a filter is to load the whole list, and determine its size by calling .size() method - this is extremely inefficient and can even cause OutOfMemoryError (e.g. a HistoryActivityInstanceQuery could return tens of thousands elements)

count() could be used with page(int firstResult, int maxResults) method to create a paginated result list where you can display the number of pages