Comment 5 for bug 856277

How to fix(more correct way):
Nux cannot get system value via gtk(nux::GetSysFont can use this
purpose?). Unity needs to notify font name to nux. nux:StaticText
has method SetFont, but this instance lives only in
nux::Button::RebuildLayout. RebuildLayout is called at nux::Button
label is changed.

Additionaly above, MultiButton is too narrow for all language.
It is proper to say that look nicely in English. However there
is no space to translate it.

Example in music lense, "90s" in English is translated to "90年代" in
Japanese. Translator needs over double space to compare to English.

Summed up above, we needs followings:
* nux::Button should have member font_string_ and SetFont method for
  label layout.
* In Unity, call nux::Button::SetFont at appropriate time. I think
  that unity::FilterBasicButton::InitTheme is good.
* MultiButton shuld not use one line to get space for all languages.
  It seems to make two raw button is nicely.