Excluded case of trying to determine mime type for empty string.

Refactored downloader for local files.

Items duplication adapted to new ideology of adding media items on the board.

Have a problem - should take care about saving original src path.

Document navigator: "Add pages from file" isn't work with old UBZ

Implemented Sankore-729 - previews images for web search results supports images, audios, videos and flash content.
Images previews is adjusted now.
Mime type detection mechanism is more common now.

Added new system util method: deleteFile.