plantuml server regressions

[VladimirAlexiev]

@arnaudroques The http://www.plantuml.com/plantuml/ server was very useful, but I now see significant regressions:

• Half the time I get 400 Bad request Your browser sent an invalid request.
• Half the time I get a broken image, or the image appears momentarily then disappears
  • I guess this is also the reason why the plantuml Chrome extension stopped working (it uses the online server to display a local puml file as a diagram)
• There are too many ads that take up horizontal space and make it hard to see my diagram. I don't mind ads taking vertical space if I can scroll and see my diagram, but taking up horizontal space makes it nearly unusable
• "Change layout" with a complex diagram (#943) results in a diagram that's too big to fit in its window; there's no horizontal scroll bar