The font settings should be merged with the Increase/Decrease Font Size commands. I am thinking that we should make the `fontSizeStyle` view state a preference to store the font size and add a new preferences for the line height and the font family. But to make things simpler, the font size preference should just be a number which is then interpreted as the size of the font in px, and the line height should also be a number (float) which is then interpreted as the line height in ems. All these preference will be added in ViewCommandsHandlers so that we can use the same functions to update the style when the preferences change.

Since we don't have an UI for the preferences I am not sure if we should keep the UI used with the themes or just don't use any UI at the moment.