-in hill.cpp:inverse() there are some matrices of which the inverse does exist, but i can't find it, because in these matrices there is at least a column in which all the elements don't have the multiplicative inverse. ->done :-)
-in hill.cpp : encrypt and decrypt are exactly the same, except encipher/decipher. Factorise the code... 
-in hill.cpp : update the explain() method
-use the status bar
-in byteAdd and byteXor ciphers make the hexeditor-like mdichild window
-make options in mainWindow private and make the methods to access
-make possible to save new default options
-in about read the version from a file VERSION
-make possible change the language from the options