add some minimum sizies for some windows (#3333)

src/gui/dialogs/about_dialog.ui

@@ -10,6 +10,12 @@
     <height>357</height>
    </rect>
   </property>
+  <property name="minimumSize">
+   <size>
+    <width>558</width>
+    <height>357</height>
+   </size>
+  </property>
   <property name="windowTitle">
    <string>About LMMS</string>
   </property>

src/gui/dialogs/export_project.ui

@@ -10,6 +10,12 @@
     <height>412</height>
    </rect>
   </property>
+  <property name="minimumSize">
+   <size>
+    <width>519</width>
+    <height>412</height>
+   </size>
+  </property>
   <property name="windowTitle">
    <string>Export project</string>
   </property>

src/gui/widgets/ControllerRackView.cpp

@@ -89,6 +89,7 @@ ControllerRackView::ControllerRackView( ) :
 	subWin->move( 680, 310 );
 	subWin->resize( 350, 200 );
 	subWin->setFixedWidth( 350 );
+	subWin->setMinimumHeight( 200 );
 }