new resources for linux software package managers

Package managers like Matt Caraldo (https://launchpad.net/~bitcoin/+archive/bitcoin) should now include the new png icons in their bitcoin linux .deb files.
The current xpm file bitcoin80.xpm (80x80px) was deleted because it contains a non-stamdard size.
I've testes with png files and did figure out the png files as icons will resize proper while xpm files will end up in non-resizing menu items which then can result in gfx bugs like reported with #2543.
I recommend to use png files as pixmaps in upcoming linux software packages.

- new xpm resources for different linux window managers
- new png files for autoresizing on different linux window managers
- favicon with new logo
- window .ico with new logo