Website updates for LO 7.1 release and localisation

l10n
#1

Hi everyone,

For the LO 7.1 release today I'll update the EN website accordingly. My
changes are below -- feel free to implement them on other language
websites too. Thanks a lot for all your help!

1) Update "7" to "7.1" on https://www.libreoffice.org

2) Update https://www.libreoffice.org/download/release-notes/ to reflect
the new "Fresh" and "Still" branches

3) Update https://www.libreoffice.org/discover/new-features/ with text
underneath

4) Update https://www.libreoffice.org/about-us/libreoffice-timeline/
(and add info about LibOCon -- thanks Raal for the reminder)

New text for point 3:

Faster, smoother, smarter

LibreOffice 7.1 includes performance improvements across the board:
find/replace operations, spell-checking, autofilter, and more. New
physics-based animation effects and soft-blurred shadows make your
presentations stand out. And new table and spreadsheet functions help
you to handle data more effectively.

Work with more documents

LibreOffice uses the standardised OpenDocument format - a great choice
for long-term data storage. But it can also open Microsoft Office
documents, and LibreOffice 7.1 brings many improvements to compatibility
here: change tracking in floating tables, formula import in text tables,
and export of formula fields.

Choose an interface customised for you

When first started, LibreOffice 7.1 presents a new user interface
selection dialog. You can choose between the "classic" menu+toolbar
layout, or opt for the newer NotebookBar design, which is also available
in the menu via View > User Interface > Tabbed.

Further details

For a full list of new features in LibreOffice 7.1, see our release notes.