Rename "Our Goal" to "Our Mission"
Web: Reorder Introduction contents

Menu structure matches the structure of the boxes.

There are some things I would like to do but don't dare without
prior discussion (in whatever circle and form):

TODO: I would really like to move Essay to Introduction and
replace the Background menu intem with that.
It has to be discussed if it can be moved away from Manuals
(it can still be linked from there but would be purged from the menu

TODO: I would like to Move Productions and Reviews to Community.
Web: Restructure "Features" page outline

This doesn't modify the content, although I have a clear idea about them.
So some contents don't seem to fit to the headings.
Web: Extend and rewrite Features->Text input
Web: Rewrite and Extend Features->Usability
Web: Rewrite and Ext. Features->Extensible design
Web: Rewrite and Extend Features->Environment
Web: Add introduction to "Download" page
Web: Remove previous warning on "Download" pages

The note about LilyPond being a text based tool has been
replaced by a more explicit introductory section.

I think this makes the warning also obsolete on the subpages
because one will only reach the "Unix" (e.g.) page through the
main "Download" page.
Web: Add introduction to "Editing" page.
Web: Editing: Make Tunefl the last editor

I think Tunefl should get into a new section "Online Tools"

As long as that isn't decided I want to have it out of the way.
Web: Editors: Move LilyPondTool to discontinued

Keep the clickable image although until now there haven't been
images in that section.
But I think that's justified as LilyPondTool is still usable.
Web: Editing: Update Frescobaldi section
Web: Editing: Add Heading
Web: Editing: Rewrite Denemo section
Web: replace "Still not convinced?" with "Not convinced yet?"

"Still not convinced?" sounds a bit as if we said "you're stubborn!".
Web: Some rewordings and shortenings
Web: Editors: Add "Web frontends" section

TODO: Add screenshots for the tools
Web: Editing: Add links to subsections in intro
Revert "Web: Remove previous warning on "Download" pages"

This reverts commit f1cdf9b670e8917e4c5412a107c4b703b45a42a3.