Fix some chat right pane issues

- Remove the default Qt dragMargin: when the right pane was
  hidden/collapsed in the interface, accidentally clicking on this
  invisible 10 pixel-wide zone to the right edge of the window
  would interfere with any button under it, e.g. the button to
  expand the pane

- Fix expand pane button failing to bring back pane (due to dragMargin)
  and turning the chat page header invisible

- Disable swiping to exit panes, interferes with buttons and tiles

src/gui/Base/HDrawer.qml

@@ -81,8 +81,10 @@ Drawer {
 
     // FIXME: https://bugreports.qt.io/browse/QTBUG-59141
     // dragMargin: parent.width / 2
+    // interactive: collapse || forceCollapse
+    dragMargin: 0
+    interactive: false
 
-    interactive: collapse || forceCollapse
     position: 1
     visible: ! collapse && ! forceCollapse
     modal: false

src/gui/Pages/Chat/RoomHeader.qml

@@ -22,13 +22,6 @@ Rectangle {
     HRowLayout {
         id: row
         anchors.fill: parent
-        visible: opacity > 0
-
-        // The layout overflows somehow when focusing the room pane and
-        // is visible behind it (with a transparent theme)
-        opacity: showRightButton && chat.roomPane.visible ? 0 : 1
-
-        Behavior on opacity { HNumberAnimation {} }
 
         HButton {
             id: goToMainPaneButton