Decide about default package banners

[ThomasBreuer]

Default package banners show more information than in earlier GAP versions
since pull request #3215 has been merged.

In the discussion about that pull request, it turned out
that more informative package banners can on the one hand be useful,
but on the other hand this may be not what one wants to be shown by default in any GAP session.

One should have in mind that loading a package during a session likely causes
several other packages to be loaded, and all their banners are shown.

Of course one can suppress banners completely, via the command line option -b,
and this had been my favorite setup for a long time.
However, it is often useful to know the current version numbers of packages,
in particular if one works with different versions of GAP --development version
and the latest two releases, say-- and their sets of packages.

My proposal (collected from the discussion of #3215) would be as follows.

• In a classical GAP session in a terminal, let LoadPackage by default show a short summary of the names and version numbers of those packages that were loaded anew, analogous to the overview of autoloaded packages in the GAP banner.
  (Note that the current GAP banner is quite modest, compared to the banners from the early times of GAP 4 or even GAP 3 --these earlier GAP banners gave the message that now GAP is coming and anything else should disappear from the screen.)

• Provide a GAP function that prints or returns the current banner of a given package (the ``full package banner''), such that the user can get this information in cases where this is interesting.

• In Jupyter notebooks or similar environments, show the same as in the GAP session but support ``unfolding'' the full package banner on clicking the package name/version part in the shown summary.

• Perhaps introduce a user preference that changes the default in order to let LoadPackage show full package banners.

• The outpout shown by the function BrowseGapPackages can be extended by clickable entries for showing the full package banner, and for opening the relevant URLs in a browser.