Custom Main Toolbar drawer visual improvements

Drawer now affected by theme, consistent with the rest of the active elements.

TODO: Add hover for desktop

custom-example/res/Custom/Widgets/CustomToolBarButton.qml

@@ -22,7 +22,8 @@ Button {
 
     background: Rectangle {
         anchors.fill:               parent
-        color:                      mouseArea.pressed ? qgcPal.buttonHighlight : Qt.rgba(0,0,0,0)
+        color:                      qgcPal.buttonHighlight
+        visible:                    (mouseArea.pressed || button.checked)
     }
 
     contentItem: Row {
@@ -40,7 +41,7 @@ Button {
             width:                  height
             sourceSize.height:      parent.height
             fillMode:               Image.PreserveAspectFit
-            color:                  (mouseArea.pressed || button.checked) ? qgcPal.primaryButton : qgcPal.buttonText
+            color:                  qgcPal.buttonText
             source:                 button.icon.source
             anchors.verticalCenter: parent.verticalCenter
         }
@@ -48,7 +49,7 @@ Button {
             id:                     _label
             visible:                text !== ""
             text:                   button.text
-            color:                  (mouseArea.pressed || button.checked) ? qgcPal.primaryButton : qgcPal.buttonText
+            color:                  qgcPal.buttonText
             anchors.verticalCenter: parent.verticalCenter
         }
     }

custom-example/res/MainToolbar/CustomMainToolBar.qml

@@ -169,10 +169,10 @@ Item {
         }
         ColumnLayout {
             id:                             buttons
+            spacing:                        0
             anchors.top:                    parent.top
             anchors.left:                   parent.left
             anchors.right:                  parent.right
-            spacing:                        ScreenTools.defaultFontPixelHeight * 0.125
             Rectangle {
                 Layout.alignment:           Qt.AlignVCenter
                 width:                      parent.width
@@ -181,6 +181,7 @@ Item {
             }
             CustomToolBarButton {
                 id:                         flyButton
+                spacing:                    1
                 text:                       qsTr("Fly")
                 icon.source:                "/qmlimages/PaperPlane.svg"
                 Layout.fillWidth:           true
@@ -254,10 +255,9 @@ Item {
         ColumnLayout {
             id:                             lowerButtons
             anchors.bottom:                 parent.bottom
-            anchors.bottomMargin:           ScreenTools.defaultFontPixelHeight * 0.125
             anchors.left:                   parent.left
             anchors.right:                  parent.right
-            spacing:                        ScreenTools.defaultFontPixelHeight * 0.125
+            spacing:                        0
             Rectangle {
                 Layout.alignment:           Qt.AlignVCenter
                 width:                      parent.width