Rewrite setup wizard

[n0phx]

Current setup wizard is an overgrown stack of patches and extensions, needs a fresh start:

• Utilize class based route handlers instead of current hackish class solution
• Preferably move the task of step collection to the collector code completely, removing the logic of registration, etc from the wizard itself
• Retain feature of storing the state in both session and disk because currently session storage allows the number of steps not to drop between steps while using the wizard, while disk storage does not protect against that, but it can load a fresh instance of the wizard with only the remaining-not done steps