refs #768, improved selectors

* added focus proxy
* using &QLineEdit::editingFinished as signal (changes value also when focus is lost)
* use enum to set how values are displayed
* search for DB values by leveraging the smart selector functions
* added isSet functions
* minor renamings/formatting

src/blackgui/components/dbaircrafticaoselectorcomponent.ui

@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>189</width>
-    <height>22</height>
+    <height>24</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -57,6 +57,9 @@
    </item>
   </layout>
  </widget>
+ <tabstops>
+  <tabstop>le_Aircraft</tabstop>
+ </tabstops>
  <resources/>
  <connections/>
 </ui>