WelcomeScreen: disable horizontal scrollbars for listviews

When customizing background color of a widget via CSS, Qt somehow
falls back to ugly old windows style. This resulted in ugly looking
scrollbars in WelcomeScreen when working at a low screen resolution.
Therefore disable those scrollbars as they're rather useless anyways.
QListView automatically shows three dots for too wide text items.

src/gui/Forms/WelcomeScreen.ui

@@ -356,6 +356,9 @@ p, li { white-space: pre-wrap; }
           <property name="verticalScrollBarPolicy">
            <enum>Qt::ScrollBarAlwaysOff</enum>
           </property>
+          <property name="horizontalScrollBarPolicy">
+           <enum>Qt::ScrollBarAlwaysOff</enum>
+          </property>
           <property name="iconSize">
            <size>
             <width>16</width>
@@ -375,6 +378,9 @@ p, li { white-space: pre-wrap; }
           <property name="verticalScrollBarPolicy">
            <enum>Qt::ScrollBarAlwaysOff</enum>
           </property>
+          <property name="horizontalScrollBarPolicy">
+           <enum>Qt::ScrollBarAlwaysOff</enum>
+          </property>
           <property name="iconSize">
            <size>
             <width>16</width>