Update all tutorials Unified Installer + ZopeSkel based

[miohtama]

All tutorials should be based on Unified installer and ZopeSkel, as that what novice users use. No custom buildouts or virtualenvs allowed.

[miohtama]

Check if unified installer indeed comes with ZopeSkel

Update all tutorials on d.p.o to use ZopeSkel and Unified Installer

Make sure tutorials work in Windows

[miohtama]

Unified installer comes with ZopeSkel

[cewing]

This would seem to indicate that the installer includes ZopeSkel