Modified IOptionsPage interface for Apply button

The previous interface wasn't sufficient to properly support the Apply
button, since it didn't separate applying the changes from the cleanup
phase.

Designer settings pages still need some fixing.

Fixes Apply button causing problems for certain plugins, for example the
QuickOpen.

src/plugins/texteditor/fontsettingspage.cpp

@@ -435,13 +435,8 @@ void FontSettingsPage::delayedChange()
     emit changed(d_ptr->m_value);
 }
 
-void FontSettingsPage::finished(bool accepted)
+void FontSettingsPage::apply()
 {
-    if (!accepted) {
-        d_ptr->m_value = d_ptr->m_lastValue;
-        return;
-    }
-
     d_ptr->m_value.setFamily(d_ptr->ui.familyComboBox->currentText());
 
     bool ok = true;
@@ -460,6 +455,12 @@ void FontSettingsPage::finished(bool accepted)
     }
 }
 
+void FontSettingsPage::finish()
+{
+    // If changes were applied, these are equal. Otherwise restores last value.
+    d_ptr->m_value = d_ptr->m_lastValue;
+}
+
 const FontSettings &FontSettingsPage::fontSettings() const
 {
     return d_ptr->m_value;