Thread TypeScript semantic errors as warnings

Fixes http://teampulse.telerik.com/view#item/282195
What will happen in case there are nonEmitPreventingWarningCount errors and hasPreventEmitErrors = true? From the code it looks like errorTitle will be set to nonEmitPreventingWarining errors and the process will fail with message including only them. Maybe we should compose more complex errorTitle, showing all errors? What do you think?