remove setStyleSheet calls directly from widget code

removed from:
 - emoji panel scrollbars
 - emoji category labels
 - splitter image handles
 - textfield setTextColor impl

small change to the category separator label for better contrast /
readability in dark mode.

removed setTextColor completely from TextField. Doesn't appear to be in
use anywhere, and focus going more toward qss themeing from qproperty
setting.

src/ui/TextField.cpp

@@ -102,23 +102,6 @@ TextField::label() const
         return label_text_;
 }
 
-void
-TextField::setTextColor(const QColor &color)
-{
-        text_color_ = color;
-        setStyleSheet(QString("QLineEdit { color: %1; }").arg(color.name()));
-}
-
-QColor
-TextField::textColor() const
-{
-        if (!text_color_.isValid()) {
-                return QPalette().color(QPalette::Text);
-        }
-
-        return text_color_;
-}
-
 void
 TextField::setLabelColor(const QColor &color)
 {