Fix Connections deprecation warning on Qt 5.15

Adopt the correct behavior to get rid of
"QML Connections: Implicitly defined onFoo properties in Connections
 are deprecated. Use this syntax instead:
 function onFoo(<arguments>) { ... }"

src/gui/Base/HTile/HTile.qml

@@ -50,7 +50,8 @@ HButton {
     Connections {
         enabled: contextMenuLoader.status === Loader.Ready
         target: contextMenuLoader.item
-        onClosed: contextMenuLoader.active = false
+
+        function onClosed() { contextMenuLoader.active = false }
     }
 
     HLoader {

src/gui/Base/MediaPlayer/VideoPlayer.qml

@@ -42,7 +42,8 @@ Video {
 
     Connections {
         target: mainUI.fullScreenPopup
-        onClosed: fullScreen = false
+
+        function onClosed() { fullScreen = false }
     }
 
     TapHandler {

src/gui/MainPane/RoomList.qml

@@ -199,9 +199,11 @@ HListView {
 
     Connections {
         target: pageLoader
-        onPreviousShown:
+
+        function onPreviousShown(componentUrl, properties) {
             if (setCorrectCurrentItem() === false) startCorrectItemSearch()
         }
+    }
 
     Timer {
         // On startup, the account/room takes an unknown amount of time to

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

@@ -71,9 +71,10 @@ MultiviewPane {
     Connections {
         target: swipeView
 
-        onCurrentItemChanged:
+        function onCurrentItemChanged() {
             swipeView.currentItem.keybindFocusItem.forceActiveFocus()
         }
+    }
 
     MemberView {}
     SettingsView {}

src/gui/Pages/Chat/Timeline/EventContent.qml

@@ -171,11 +171,16 @@ HRowLayout {
 
             Connections {
                 target: eventList
-                onCheckedChanged: contentLabel.deselect()
-                onDelegateWithSelectedTextChanged:
+
+                function onCheckedChanged() {
+                    contentLabel.deselect()
+                }
+
+                function onDelegateWithSelectedTextChanged() {
                     if (eventList.delegateWithSelectedText !== model.id)
                         contentLabel.deselect()
                 }
+            }
 
             HoverHandler { id: contentHover }