Add new admin widget "Community message"

[tobifjellner]

WordPress regularly gets translated into some 50-60 language versions. But it could be more. (Ref: ​https://make.wordpress.org/polyglots/teams/ )

We've got a long list of local WordPress forums in various languages. But not all of them are active, and there could be more languages here, too.
(Ref: ​https://make.wordpress.org/support/handbook/contributing-to-the-wordpress-forums/support-forums-in-your-language/ )

From time to time, there are other things happening, where it would be good to have a reasonably prominent place to make a message visible to people that use WordPress in a specific language.

Yes, we are able to "reuse" the two RSS feeds in the Admin widget "WordPress events and News", but ever since this widget also started housing notices about meetups and WordCamps, the news only show the title and barely gets noticed.

So I'd like to propose that we in the Admin panel add a new widget "Community" where contributors can put one formatted message that may change from time to time.

Perhaps some "hack" via translate.wordpress.org could work as handling mechanism. (But it would be good to NOT depend on core language packs, since those get generated only when core is 100% translated. If a GTE would like to publish a "call for help" they'd be forced to first reach 100% translation status before they'd be able to get this message distributed...)

This could prove a vital tool to strengthen the continuity in many locales, where currently there are only 1-2 General Translation Editors each that keep everything rolling. There may formally be more people listed, but due to the very nature of volunteer contributions, not all are actively contributing.

[fierevere]

Something rendered like "welcome" page on /team p2, will be nice to have.
(Optionally - dismissable by user?).

With Locale Manager ability to enable/disable/edit message.

PS: meant more a rosetta sites widget, such as call-to-action banner for surveys, but with more space for text. Maybe worth another ticket for meta?

Dashboard widget will be nice to have too, not all locales use even 1 RSS channel, but sometimes this feature is very needed.