v0.51

Sabine 0.51

• Fix Sabine apps crashing as they quit on Linux, most often with NVIDIA's driver, sometimes
  reported as "double free or corruption". The window tore its graphics device down on another
  thread while the process was already exiting, so the driver freed its own state twice. The
  window now destroys its device before it exits, and quitting an app ends it with status 0.
• An app stopped with SIGTERM or SIGINT, such as by a system monitor or systemctl stop, ends
  by that signal instead of exiting with a status, so whatever stopped it sees that it did.
• Tapping or clicking into a text field on Linux asks the desktop for its on-screen keyboard.
• An app no longer claims the shared Sabine host is out of date when another copy of the app,
  running with another version of Sabine, has its data open. The window says so and asks to close
  the other copy, and says the app needs another version of Sabine only when its own host doesn't
  match. A shared Chromium left over from another Sabine build hands the window to the app's own
  Chromium, and a browser connection that breaks while it starts is retried.