prettify preferences dialog

coverart_search_providers.plugin

@@ -1,5 +1,5 @@
 [Plugin]
-Loader=python
+Loader=python3
 Module=coverart_search_providers
 IAge=2
 Depends=rb

ui/coverart_search_providers_prefs.ui

@@ -60,6 +60,10 @@
             <property name="can_focus">False</property>
             <property name="xalign">0</property>
             <property name="label" translatable="yes">Choose Search Providers:</property>
+            <attributes>
+              <attribute name="weight" value="bold"/>
+            </attributes>
+            <property name="margin_bottom">15</property>
           </object>
           <packing>
             <property name="expand">False</property>
@@ -71,6 +75,7 @@
           <object class="GtkGrid" id="grid1">
             <property name="visible">True</property>
             <property name="can_focus">False</property>
+            <property name="margin_left">30</property>
             <child>
               <object class="GtkTreeView" id="provider_list">
                 <property name="height_request">200</property>