UI: Fix spacing with media controls

The spacing in the media controls was set to 0. This only became
noticeable when using the Yami theme, as the buttons have a background
color.

UI/forms/source-toolbar/media-controls.ui

@@ -27,7 +27,7 @@
   </property>
   <layout class="QHBoxLayout" name="horizontalLayout">
    <property name="spacing">
-    <number>0</number>
+    <number>6</number>
    </property>
    <property name="leftMargin">
     <number>0</number>
@@ -82,22 +82,6 @@
      </property>
     </widget>
    </item>
-   <item>
-    <spacer name="horizontalSpacer">
-     <property name="orientation">
-      <enum>Qt::Horizontal</enum>
-     </property>
-     <property name="sizeType">
-      <enum>QSizePolicy::Fixed</enum>
-     </property>
-     <property name="sizeHint" stdset="0">
-      <size>
-       <width>8</width>
-       <height>20</height>
-      </size>
-     </property>
-    </spacer>
-   </item>
    <item>
     <widget class="QPushButton" name="previousButton">
      <property name="sizePolicy">
@@ -243,22 +227,6 @@
      </property>
     </widget>
    </item>
-   <item>
-    <spacer name="horizontalSpacer_2">
-     <property name="orientation">
-      <enum>Qt::Horizontal</enum>
-     </property>
-     <property name="sizeType">
-      <enum>QSizePolicy::Fixed</enum>
-     </property>
-     <property name="sizeHint" stdset="0">
-      <size>
-       <width>6</width>
-       <height>20</height>
-      </size>
-     </property>
-    </spacer>
-   </item>
    <item>
     <widget class="QLabel" name="timerLabel">
      <property name="sizePolicy">
@@ -278,22 +246,6 @@
      </property>
     </widget>
    </item>
-   <item>
-    <spacer name="horizontalSpacer_3">
-     <property name="orientation">
-      <enum>Qt::Horizontal</enum>
-     </property>
-     <property name="sizeType">
-      <enum>QSizePolicy::Fixed</enum>
-     </property>
-     <property name="sizeHint" stdset="0">
-      <size>
-       <width>4</width>
-       <height>0</height>
-      </size>
-     </property>
-    </spacer>
-   </item>
    <item>
     <widget class="QLabel" name="label">
      <property name="sizePolicy">
@@ -313,22 +265,6 @@
      </property>
     </widget>
    </item>
-   <item>
-    <spacer name="horizontalSpacer_4">
-     <property name="orientation">
-      <enum>Qt::Horizontal</enum>
-     </property>
-     <property name="sizeType">
-      <enum>QSizePolicy::Fixed</enum>
-     </property>
-     <property name="sizeHint" stdset="0">
-      <size>
-       <width>4</width>
-       <height>0</height>
-      </size>
-     </property>
-    </spacer>
-   </item>
    <item>
     <widget class="ClickableLabel" name="durationLabel">
      <property name="sizePolicy">