Rework HBox-based pages and account settings

- Refactor everything about HBox, and adapt all the pages and popups
  that used it

- Replace HTabContainer by HTabbedBox

- Make boxes swippable

- Make esc presses in boxes click the cancel button

- Make all boxes and popups scrollable when needed

- Replace generic apply button icons in popups

- Fix tab focus for error and invite popups

- Rework (still WIP) the account settings page:
  - Use the standard tabbed design of other pages
  - Ditch the horizontal profile layout, hacky and impossible to extend
  - Add real-time coloring for the display name field

- Implement a device list in account settings (Sessions, still WIP)

src/gui/Pages/Chat/RoomPane/SettingsView.qml

@@ -57,9 +57,6 @@ HFlickableColumnPage {
     }
 
 
-    useVariableSpacing: false
-    column.spacing: theme.spacing * 1.5
-
     flickShortcuts.active:
         ! mainUI.debugConsole.visible && ! chat.composerHasFocus
 
@@ -82,6 +79,8 @@ HFlickableColumnPage {
         }
     }
 
+    Keys.onEscapePressed: cancel()
+
 
     HRoomAvatar {
         id: avatar