Introduced "TaskPriority" enum and "AsyncTask.Priority" property
Implemented "GetPriorityCore" for all "AsyncTask" derived classes
Implemented "GetPriorityCore" for all "AsyncTask" derived classes
Updated "ReprioritizeTasksInQueue" to cater for "AsyncTask.Priority"
Updated "TestTaskStateChangedEventHandling" to inter-mix tasks
Implemented a stub test class for AggregateRenderPackageAsyncTask
Implemented "StubAsyncTask" as wrapper of actual AsyncTask classes
Implemented skeleton "SchedulerIntegrationTests" class
Implemented "SchedulerIntegrationTests.WrapXyzAsyncTask" methods
Added "UpdateRenderPackageAsyncTask.nodeGuid" for identity
Implemented a failed test case "TestTaskQueuePreProcessing00"
Updated "TestTaskQueuePreProcessing00" test with expected results
Implemented "AggregateRenderPackageAsyncTask.CanMergeWithCore"
Implemented "CanMergeWithCore" method for some "AsyncTask" classes
Replaced "StubAsyncTask" with actual async task derived classes
Added two more test cases to "SchedulerIntegrationTests"
Replaced "AsyncTask.GetPriorityCore" with "AsyncTask.Priority" property
Addressed review comments (renaming AsyncTask test classes)
Merge pull request #2874 from Benglin/Revit2015

Cross merging master changes into Revit 2015