provide UI for multi-column and justified margin support

[karlkleinpaste]

Although the code exists to use ~/.xiphos/default.css and per-module style.css in the module's DataPath, there is no way for the user to employ this without editing it directly. But the most common uses could be provided without having to bother with these files at all. Specifically, the UI should provide for multi-column rendering and margin justification. With today's very large screens, single column output can become very unreadable, so this helps the eye not get lost in very long horizontal rendering.

Prefs dialog enhanced to show default columns selector (1-4) in the "fonts" page, as well as a "justify margins" checkbox. On a per-module basis, the font selection dialog has gained a column selector. No margin justification is there, as that seems an unlikely use: Few users will want margin justification only some of the time, while many modules will have specific column needs such as when a genbook is being displayed alone. Tooltips in the prefs dialog point the user to per-module specificity in font selector.

default.css and style.css are still present for the user to play with, for whatever other effects he might want.