Multi device support: add start/stop buttons to all source plugins GUIs

plugins/samplesource/rtlsdr/rtlsdrgui.ui

@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>287</width>
+    <width>298</width>
     <height>271</height>
    </rect>
   </property>
@@ -34,6 +34,18 @@
    </property>
    <item>
     <layout class="QHBoxLayout" name="horizontalLayout_freq">
+     <item>
+      <widget class="ButtonSwitch" name="startStopButton">
+       <property name="text">
+        <string/>
+       </property>
+       <property name="icon">
+        <iconset resource="../../../sdrbase/resources/res.qrc">
+         <normaloff>:/play.png</normaloff>
+         <normalon>:/stop.png</normalon>:/play.png</iconset>
+       </property>
+      </widget>
+     </item>
      <item>
       <spacer name="horizontalSpacer">
        <property name="orientation">
@@ -451,6 +463,8 @@
    <header>gui/buttonswitch.h</header>
   </customwidget>
  </customwidgets>
- <resources/>
+ <resources>
+  <include location="../../../sdrbase/resources/res.qrc"/>
+ </resources>
  <connections/>
 </ui>