Overview of changes in simple-scan 3.25.2

  * Redesign preferences dialog.
  * Move JPEG compression control to save dialog.
  * Replace blank page with a homescreen that shows scanner status.
  * Simplify header bar controls.
  * Move page controls to an action bar below scanned page.
  * Improve algorithm that picks JPEG or zlib compression for PDF files.
  * Restrict image file filter to supported image formats.
  * Fix compilation with Vala 0.36.
  * Remove obsolete code.