Improve UI for Preferences button

Add a text so there's not just a (potentially missing) icon, also use
a different icon that's also available in Adwaita icon theme.

ui/razergenie.ui

@@ -64,14 +64,26 @@
            <verstretch>0</verstretch>
           </sizepolicy>
          </property>
+         <property name="minimumSize">
+          <size>
+           <width>150</width>
+           <height>0</height>
+          </size>
+         </property>
+         <property name="maximumSize">
+          <size>
+           <width>150</width>
+           <height>16777215</height>
+          </size>
+         </property>
          <property name="toolTip">
-          <string>Preferences</string>
+          <string/>
          </property>
          <property name="text">
-          <string/>
+          <string>Preferences</string>
          </property>
          <property name="icon">
-          <iconset theme="preferences-system"/>
+          <iconset theme="preferences-system-symbolic"/>
          </property>
          <property name="iconSize">
           <size>
@@ -80,10 +92,26 @@
           </size>
          </property>
          <property name="flat">
-          <bool>true</bool>
+          <bool>false</bool>
          </property>
         </widget>
        </item>
+       <item>
+        <spacer name="horizontalSpacer">
+         <property name="orientation">
+          <enum>Qt::Horizontal</enum>
+         </property>
+         <property name="sizeType">
+          <enum>QSizePolicy::Maximum</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>8</width>
+           <height>1</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
        <item>
         <widget class="QLabel" name="versionLabel">
          <property name="text">