HaikuDepot: Improve filter UI, fix pkg translations

 * The categories and other filter options are orthogonal. Don't
   force the user to choose between real categories and for example
   "installed" or "available" in the same drop-down. I've removed
   (for now) the Options main menu. There are now four small check-marks
   below the filtering drop-downs: Available, Installed, Development and
   Source Code. These enable showing the respective packages in the list
   view. Only "Available" is checked by default. This changes the default
   behavior to show only not-yet-installed packages. This change puts
   the filtering options in one place, the showing of development or
   source code packages is not "hidden somewhere else" anymore. I am not
   so happy with the additional row, however, I am also thinking about
   using icons instead of the checkmarks.
 * Fixed finding the suitable package translation for summary and
   description. For example, WonderBrush now has a German translation.
HaikuDepot: Fixed reading bigger screenshots

 * Increase the RAM limit to 128K per screenshot
 * Reduce retrieved size to 320 pixel wide
 * Don't expect to be able to read the stream in one call,
   read it in 4K chunks.
 * Print some errors in this code-path to stderr.