Extend Algorithm base class to allow algorithms to execute asynchronously

[Nick Draper]

The base class should be extended to add an ExecuteAsync method. This should run the Exec method in a separate thread and communicate the result back through some callback mechanism (Boost.Signals?).

Once this works the QTIPLOT interface should be altered to use this as the primary method of running algorithms.

[Roman Tolchenov]

(In [1300]) re #203. New Algorithm::executeAsync() method runs the algorithm in a separate thread. It posts Poco::Notifications when it starts and finishes and also when an exception is thrown. Algorithms can send notifications about their progress by calling Algorithm::progress() method.

[Roman Tolchenov]

(In [1301]) re #203. Asynchronous execution test.

[Roman Tolchenov]

(In [1302]) re #203. Qtiplot runs algorithms asynchronously.

[Roman Tolchenov]

(In [1303]) re #203. Fix to qtiplot build

[Roman Tolchenov]

(In [1306]) re #203. Correction to AsynchronousTest.h

[Roman Tolchenov]

(In [1311]) Improved Algorithm::cancel() to be able to stop execution when a child algorithm is running. Fixes to windows installer. refs #203, #213

[Russell Taylor]

(In [1312]) Updates to test scripts following asynchronous Algorithm extension. Re #203.

[Roman Tolchenov]

(In [1318]) Fixed bugs. re #203

[Roman Tolchenov]

(In [1340]) Added AlgorithmMonitor class to qtiplot which monitors all running algorithms. re #203

[Stuart Campbell]

This ticket has been transferred to github issue ​1051