[UPDATE] Better error handling for the IncludeViewhelper

If the Package/Controller is unknown the whole site will just show a big TYPO3.Flow
error message. This patch introduces the viewhelper argument "exceptionAs", this will make
it possible to display a custom error message in place of the plugin.

<mdc:include package="Kollode.TestPlugi" controller="Standard" action="index" exceptionAs="exception">
	<div data-alert class="alert-box alert">{exception.message}</div>
</mdc:include>

I also looked into the handling of 500 or 400 errors, but that seems to be just Flow configurations,see TYPO3.Flow -> Settings.yaml -> exceptionHandler