Introduce JOSM plugins on the Startup page

[sano]

I have two motivations for opening this ticket:

1. I am a long time ​JOSM user, but have not investigated systematically what good the plugins available to me can do for me. I recall that during my tenure I have visited the plugin list just a handful of times to address a specific editing need I had at the moment. I suspect that my story is not unique and think that as a result we, JOSM editors, are not as efficient in our work as we could be. I think we could improve the situation by giving the plugin creators an option to create a succinct description of their plugin functionality, maybe in the form of a short description, slideshow or a video and display such information on the Startup page.
2. Recently I have sponsored development of the Rovas Connector Help/Plugin/RovasConnector plugin and realized that the likely best way to let the JOSM users become aware of its existence would be to have it's description appear on the Startup page.

I imagine the mechanism could work this way:

The Startup page would gain a new block right above the news feed that would show information about a Featured plugin. I imagine JOSM would use an algorithm of some kind to pick one from all of the available plugins, to be shown during a certain time period.
The block would contain the kind of description I mention in the point No. 1 above and the plugin developers would be responsible for creating the content. For this purpose a specifically tagged section on the plugin wiki page could be created that would contain a condensed description of the plugin. Optionally JOSM code could display the whole plugin wiki page, if it did not detect presence of such a section.

In addition, the Startup page could show another block, shown when new plugin becomes available. Such New plugin block would use the same information the Featured plugin block provides. The New plugin would also be displayed only for one cycle and then removed from the Startup screen.