Removable storage

[bell07]

Hopefully the last big thing. The items handling is implemented. This PR contains:

• A lot of API breaks and enhancements
• Floppy/USB-Stick removable Item #46
• Storage framework and removable manager app #17
• Different capabilities each computer definition (hdd, floppy, usb, net, floppy-boot)
• Backup/Restore Computer on USB-Stick in removable manager app
• Old computers can boot from floppy
• Save as/load file dialog
• Support for per theme node coloring (Palette still missing) #34
• Sticky Notepad App: can save/load files on hdd and on floppy/usb-stick #43
• Mail-App: Simple select the mail receiver from dropdown