Make the command line editable

The user can now edit the command line (when inputting commands or making a search).
  * This can be done by either:
     -  clicking the command line;
     -  pressing ARROW LEFT (goes to the end);
     -  pressing HOME (goes to the beginning).
  * The edition can be terminated by:
     - pressing ESC,
     - deleting everything (BACKSPACE)
     - executed by pressing RETURN
  * Since the command line is just a regular textbox, clipboard access becomes a handy bonus ;)

Signed-off-by: Antonio Inacio <ja.te.disse@hotmail.com>