Update About page

[hahn-kev]

The about page is quite out of date, it should be updated to reflect the current state of support.

Here's the current version

how do we want to update this?

[papeh]

How's this? (Dates, etc., should be stamped by CD builds.) I've tweaked some wording and added a link to Lexbox. I've left the original three with first billing.

#430

[papeh]

Also credited the Lexbox team and removed links to palaso.org (redirects to softtware.sil.org)