Add task tracking flag

[georgejecook]

We should have a mechanism for knowing how many tasks are currently running. Proposal:**

New debug flag: trackActiveTasks: boolean = false

When set to true, the framework will automatically update global.runningTasks, to maintain a count of all running tasks.

This count will be increased by one, whenever a task is created. It will be decreased when the task end execution:

• by returning a value
• by being cancelled. e.g.

global: { _m_runningTasks: { ContentTask: 5 AuthTask: 2 LoggingTask: 13 TaskThatIsCausingProblems: 57 } }