#17 Change font family and weight

[Bernard Savonet]

On my machine, the mail headers appear in bold and
are less readable than I wouyld personnally prefer.

Being able to choose font size and weight (bold/ regular)
would be a great improvement for me.
Being sure that it will also be able to display correctly
any accented charaters I might get would alo be great...
but this is probably tons less essential.