qml: initial RbF bump fee feature

electrum/gui/qml/components/controls/FeeMethodComboBox.qml

@@ -0,0 +1,26 @@
+import QtQuick 2.6
+import QtQuick.Controls 2.0
+
+import org.electrum 1.0
+
+ComboBox {
+    id: control
+
+    required property QtObject feeslider
+
+    textRole: 'text'
+    valueRole: 'value'
+
+    model: [
+        { text: qsTr('ETA'), value: 1 },
+        { text: qsTr('Mempool'), value: 2 },
+        { text: qsTr('Static'), value: 0 }
+    ]
+    onCurrentValueChanged: {
+        if (activeFocus)
+            feeslider.method = currentValue
+    }
+    Component.onCompleted: {
+        currentIndex = indexOfValue(feeslider.method)
+    }
+}