Propose to install each Platform level in Windows installer.

[Zimmi48]

It was reported to me (by Pierre Rousselin) that since the Coq Platform Windows installer offers the option to unselect any unnecessary package, it can be considered annoying by the users that want a lightweight installation to unselect a lot of things. Instead, the suggestion was to propose various levels + a custom one, and it seems to me that the natural thing to do is to reuse the existing levels of the Platform, i.e.:

• base
• IDE
• full
• extended
• + custom which then would allow the user to (un)select packages manually

This reminds me of a recent similar suggestion in #278.

[MSoegtropIMC]

Triage note: this would indeed be nice to have, but it is a lot of work since the selection process in NSIS essentially has to be coded in some abstract assembly language. Set to low prio.