Keep a {id: item} cache for ModelStore models

Accelerates the ModelStore ListView find() function,
which now just has to get an object key instead of looping through the
whole model.

src/gui/Pages/Chat/Chat.qml

@@ -12,8 +12,8 @@ Item {
     property string userId
     property string roomId
 
-    property QtObject userInfo: null
-    property QtObject roomInfo: null
+    property QtObject userInfo: ModelStore.get("accounts").find(userId)
+    property QtObject roomInfo: ModelStore.get(userId, "rooms").find(roomId)
 
     property bool ready: Boolean(userInfo && roomInfo)
     property bool longLoading: false
@@ -58,22 +58,6 @@ Item {
         )
     }
 
-    Timer {
-        interval: 100
-        running: ! userInfo
-        repeat: true
-        triggeredOnStart: true
-        onTriggered: userInfo = ModelStore.get("accounts").find(userId)
-    }
-
-    Timer {
-        interval: 100
-        running: ! roomInfo
-        repeat: true
-        triggeredOnStart: true
-        onTriggered: roomInfo = ModelStore.get(userId, "rooms").find(roomId)
-    }
-
     Timer {
         interval: 300
         running: ! ready