Preferences

With this, we have and use two preferences:

1. `helios.browser.showDocOnOpen` and

2. `helios.confirmOnClose`

The default values are taken from previous versions.

`helios.confirmOnClose` has no UI but if user evaluates in workspace:

`SmalltalkSettings at: #helios.confirmOnClose put: false`

Helios will close without dialogs (and will as the usual confirm if that one stays true).