Fix conversion from font size in points to pixels.

Referencing [this](https://github.com/jaredpar/VsVim/pull/1218#issuecomment-31581114) comment.

I think I found the problem.  Visual Studio specifies the font size in points and the `FontSize` property in WPF is in pixels (see [this](http://stackoverflow.com/questions/3444371/converting-between-wpf-font-size-and-standard-font-size) StackOverflow question).

I had falsely assumed that the discrepancy I was seeing was due to the fact that I use 120 DPI (125%) instead of the default 96 DPI (100%).  However, the difference is actually due to the units, not DPI scaling.

For reference, here are new screenshots tested with Consolas 10 at both 96 DPI and 120 DPI.

96 DPI:
![image](https://f.cloud.github.com/assets/2680524/1845396/150d47e2-7586-11e3-94bb-ba07e791b739.png)

120 DPI:
![image](https://f.cloud.github.com/assets/2680524/1845397/1b160d0e-7586-11e3-8064-bd76e6c52727.png)