qml: remove implicitWidth from Continue & OutlineButton

All usage of this defines the width. This makes the buttons usable in a
wider range of situations. We keep the implicitHeight.

Author: jarolrod

src/qml/controls/ContinueButton.qml

@@ -17,7 +17,6 @@ Button {
     background: Rectangle {
         id: bg
         implicitHeight: 46
-        implicitWidth: 300
         color: Theme.color.orange
         radius: 5
 

src/qml/controls/OutlineButton.qml

@@ -18,7 +18,6 @@ Button {
     background: Rectangle {
         id: bg
         implicitHeight: 46
-        implicitWidth: 340
         color: Theme.color.background
         radius: 5
         border {