Add PCN theme system

Coexist with the old theme system for now. QML components have to be
updated to use the new system.

src/gui/Pages/Chat/Composer/Composer.qml

@@ -8,6 +8,13 @@ import "../../../Base"
 import "../AutoCompletion"
 
 Rectangle {
+    id: composer
+
+    property Theme ntheme: Theme {
+        target: composer
+        classes: Class { name: "Composer" }
+    }
+
     property UserAutoCompletion userCompletion
     property alias eventList: messageArea.eventList
 

src/gui/Pages/Chat/Composer/UploadButton.qml

@@ -8,9 +8,10 @@ import "../../../Base"
 import "../../../Dialogs"
 
 HButton {
+    ntheme.classes: Class { name: "UploadButton" }
+
     enabled: chat.roomInfo.can_send_messages
     icon.name: "upload-file"
-    backgroundColor: theme.chat.composer.uploadButton.background
     toolTip.text:
         chat.userInfo.max_upload_size ?
         qsTr("Send files (%1 max)").arg(

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

@@ -149,8 +149,6 @@ HColumnLayout {
                 HButton {
                     id: inviteButton
                     icon.name: "room-send-invite"
-                    backgroundColor:
-                        theme.chat.roomPane.bottomBar.inviteButton.background
                     enabled:
                         chat.userInfo.presence !== "offline" &&
                         chat.roomInfo.can_invite