Hi,

This patch is to fix bug #4617 and other bugs of memory window.
- Fixed bug converting to bin and hex when memory value is negative
number.
- Fixed bug to get octal number by convert from hex.
- Setting the font to fixed-width font "monospace 10"
- Adding leading zero for all of bin, oct and hex.
- Adding prefix zero to octal number.

Any suggestions are welcomed

Pearly