systemtray items respect Fitt's Law when in panel

--systemtray items are now using a rectangular form
in order to specify their hit area. So they take into
account the panel thickness in order to calculate
properly their cell length and thickness to
respect Fitt's Law. Items that are nearer to the
screen edge can now trigger all their events when
the user uses its mouse at the farest of the screen edge.

applets/systemtray/package/contents/ui/items/AbstractItem.qml

@@ -136,8 +136,8 @@ PlasmaCore.ToolTipArea {
             readonly property int size: abstractItem.inVisibleLayout ? root.itemSize : units.iconSizes.medium
 
             Layout.alignment: Qt.AlignHCenter
-            implicitWidth: size
-            implicitHeight: size
+            implicitWidth: root.vertical && abstractItem.inVisibleLayout ? abstractItem.width : size
+            implicitHeight: !root.vertical && abstractItem.inVisibleLayout ? abstractItem.height : size
             Layout.topMargin: abstractItem.inHiddenLayout ? units.smallSpacing : 0
         }
         PlasmaComponents.Label {

applets/systemtray/package/contents/ui/main.qml

@@ -156,13 +156,14 @@ MouseArea {
             interactive: false //disable features we don't need
             flow: vertical ? GridView.LeftToRight : GridView.TopToBottom
 
-            cellHeight: root.itemSize + units.smallSpacing
-            cellWidth: root.itemSize + units.smallSpacing
-
-            readonly property int columns: !vertical ? Math.ceil(count / rows)
-                                           : Math.max(1, Math.floor(root.width / cellWidth))
-            readonly property int rows: vertical ? Math.ceil(count / columns)
-                                           : Math.max(1, Math.floor(root.height / cellHeight))
+            cellHeight: vertical ? cellLength : root.height / rows
+            cellWidth: vertical ? root.width / columns : cellLength
+
+            readonly property int cellLength: root.itemSize + units.smallSpacing
+            readonly property int columns: !vertical ? Math.ceil(count / rows) :
+                                                       Math.max(1, Math.floor(root.width / cellLength))
+            readonly property int rows: vertical ? Math.ceil(count / columns) :
+                                                   Math.max(1, Math.floor(root.height / cellLength))
 
             implicitHeight: rows * cellHeight
             implicitWidth: columns * cellWidth