scanner: add a way to prune the scan process of media directories.

* If a ".mediaignore" file is present in a directory, the scan will ignore all regular files but will go through subdirectories.
* If a ".mediaignoreall" file is present in a directory, the scan will skip this directory and all subdirectories.
* ".mediaignore" or ".mediaignoreall" removal will not trigger a directory scan.
upnpsoap: Adding support to "What's new list" of Samsung TVs ES series
Samsung bookmarking: fix for magic containers
Samsung bookmark - go back to the beginning of the movie if less than 30 seconds was played.
Adding video thumbnail using libavcodec and libswscale
videothumbnail:  Makefile and configure.ac integration
videothumbnail: config integration.
videothumbnail: scanner and inotify integration

Video thumbnail is integrated in the middle of albumart creation process. Maybe later this should be moved to after the scanning procedure is finished so that the content is available ealier.
videothumbnail: better inotify integration