Add "Inspect Room Data" button in the room sidebar

I find myself doing the same routine: I want to inspect a room's state,
so I have to go hunting for the Developer Tools button. And then I have
to do a few clicks to even get the correct room, what a waste of time!

So I added a new button to the sidebar to open the Developer Tools for
the current room.

src/devtools/DevtoolsPage.qml

@@ -17,6 +17,7 @@ Kirigami.ScrollablePage {
 
     property NeoChatRoom room
     required property NeoChatConnection connection
+    property alias currentTabIndex: tabBar.currentIndex
 
     title: i18nc("@title", "Developer Tools")