Fixed \0 characters in App/Sys info string
Methods VfcHd_System.ReadSysInfo/ReadAppInfo() returned a string with \0 characters when not all characters in the string were used, which was incompatible with some python string functions (Gtk.Label.set_text() in my case). I've fixed this (now trimmed string is returned only containing used characters), simplified little bit methods around revision and info and removed HexN function, which became unused (can be easily replaced by the standard string formatting: %08x).