increase readability of fonts in dropdown menu

[jmeidal]

I feel the standard drop down menu on the toolbar could be improved. The readability is very poor because: the confined space, the preview is in a gray, the height of the font lines are very small.

I suggest:

* Increasing the line-height and font-height
* changing the preview color to a darker color (if gray is still necessary)
* increasing the width of the drop down (wider than the first item itself on the menu) to fit more characters

Using: Inkscape 0.48.4 Win32