PSR-3 logging to replace output

[SaWey]

I think it might be a good idea to change all output/print/echo calls to use the PSR-3 interface Since we want the core to be without a GUI, I think this is the way to go.

[tarekdj]

@SaWey this is a good idea since all output will be passed to GUI. So we can't rely on print/echo

[michield]

+1