Behavioral changes to KFontChooser

[Chusslove Illich]

(I wanted to make few tweaks to make it more translatable, but couldn't just
skim past the other issues, and it suckered me in...)

I consider the behavior of KFontChooser and KFontRequester at present to
have some usability problems. On top of that, there are crash situations:
e.g. in KCM Fonts, use "Set all fonts" to pick a font which doesn't have
bold style, then choose on "Window title" font (which is bold by default) --
crash.

The main usability issue I had is that the family/style/size combination in
KFontChooser need not at all times reflect an available combination, and the
preview shows something at random (e.g. when an arbitrary size is entered in
the size spinbox for non-vector font). And similarly, it is possible to
select a non-existing combo in that manner (e.g. the "Set all fonts" example
above).

The proposed fixes with the following patch (unfortunatelly longish):

http://caslav.gmxhome.de/misc/kdelibs-kdeui-fonts-2007-12-09.diff

* Make sure that an unavailable combination cannot be chosen by user or set
  by setFont methods. Make sure that the font attribute widgets at any
  moment contain only an available combination of family/style/size. Make
  sure these widgets are in perfect sync, and with the sample text.

* "Smart" browsing through families: the style and size that user explicitly
  selected are kept and always first tried when the family is switched, else
  a near match. E.g. user selects style bold, then switches to a family
  which doesn't have bold and the style reverts to regular, the switches to
  a family which has bold and the style is again shown as bold (and same for
  the size). This is for the use case of "I want a 10pt bold, let's see
  what's there."

* The style listbox double checks available styles (try set/get style and
  see if they match before showing it). Still renames Normal into Regular,
  but no longer renames Oblique into Italic (but considers them as fallback
  for each other when switching between families).

* The size listbox/spinbox operates in two modes here. When the font is
  vector, size can be chosen arbitrary in the spinbox, but make sure it's
  also displayed in the listbox; e.g. when moving from 28 (one of offered
  sizes) to 29 (not offered), insert 29 into listbox, modify this item as
  the user spins on to 30, 31, and remove it once 32 is reached (another
  offered size). When the font is bitmap, spinbox clicks move to next
  available size, not +-1; when an arbitrary value is entered, it gets
  rounded away to neareast available size.

* The sample text. No longer a QLineEdit, but a QTextEdit with vertical
  centering. So that the text wraps, shows scrollbar eventually, and the
  translators can enter multiline samples, e.g. a verse (someone inquired
  about it few months back on kde-i18n-doc). The SampleEdit widget in the
  patch does this; it has a side effect of showing window background color
  around centered text, instead of the text background, that I don't know
  how to remove (but looks kind of neat to me anyway):
  http://caslav.gmxhome.de/image/kde4-font-chooser-sampleedit-01.png

* The KFontRequester checks the font given to it, and modifies it to a near
  available match, rather then accepting as is and letting label show
  something not there. E.g. in the "Set all fonts" example above, when the
  font with no bold style is picked the "Window title" font will revert to
  regular.

This is my first involved take on GUI code (only pushing text around so
far), so don't restrain from corrective scolding.

-- 
Chusslove Illich (Часлав Илић)
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