Review default values for Settings.

The following settings have new default values for new users:

• The database file is now optimized for speed by default. (old default value: optimized for human readability)
• If less than 20 images are matched, the thumbnail view is shown. (old default value: 0)
• The thumbnail grid is now optimized for a 3:2 aspect ratio. (old default value: 4:3)
• The size of thumbnails is now 256x256 pixels. (old default value: 150)
• When starting a slideshow, it is now shown in fullscreen by default. (old default value: 800x600px)
• Detect edited images by default. Images that have been edited using the "create a copy and open" feature now are recognized by default. The tags of the original image are copied and both images are automatically stacked. (old default value: feature was not configured)