Debug output for Logic side effects

[g105b]

Logic classes should have no side effect. If they do, for example by echoing something, webengine should throw an exception

If anything is output to the buffer before the Lifecycle::finish function is called, this should be collected and output into a special debug area of the page.

Would it be nice to put it in the JavaScript console, instead of directly into the HTML? Probably...

[g105b]

This would be nice to be put into the Gt\WebEngine\Debug namespace, as we already have one with just the Timer class.

[g105b]

Now anything echoed to the page is output as a console.log, it would be nice to provide a default friendly error page and output the actual error into the JavaScript console (only developers need see it!)

[g105b]

Follows on from #299

[g105b]

Current implementation is nearly completed.

The RequestHandler::handleLogicExecution is storing the buffer correctly in the Lifecycle's debugOutput array, but still to do is understand which file's go/do functions are the trigger of the buffer. This could be done by converting LogicExecutor::invoke to a Generator function: the generator can yield a filename each time it executes the function, allowing the RequestHandler to iterate over the invoke call, adding the output buffer to the correct debug stream.