Add two-way feedback to the installer

Currently the installer either succeeds or fails.

We should improve it with these features:

- if it succeeds, add an optional link to the main website so the user:
    * is given a chance to register
    * can provide feedback on how easy the install was and what the system will be used for
    * is made aware of the support options

- if it fails, add a way to send feedback to the main site
    * maybe link to the FAQ
    * propose the support options

in this case the installer should be able to send, with the user's agreement, some data about the server and the error