Make the greeting (logo with version) in Output optional.

Original report: https://github.com/qt-labs/vstools/issues/22

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when: The non-Qt project is loaded and perhaps even a build occurs, and at this moment Qt decides that it needs to display its logo.

Describe the solution you'd like
Make Qt version information optional.