Overview of changes in simple-scan 3.25.3

  * Add support for lossy webp image.
  * More preferences dialog design improvements.
  * Make saving asyncronous, multithreaded, cancellable.
  * Add colour to scan button.
  * Put email entry in hamburger menu (was removed in design changes).
  * Don't show welcome page if autloaded document.
  * Fix scan menu not working Unity/XFCE/MATE etc.
  * Don't use headerbar on i3 desktop.
  * Set a minimal version number for packagekit-glib2.
  * Translatable string / build rules improvements.