Cleanup: renaming "frame" to "character"

The "frame" variable actually contains a string pointing to the character selected.
It has nothing to do with a frame which is usually a particular image in an animation.

I'm renaming the variable accross the application to avoid confusion.

back/src/Model/Websocket/ExSocketInterface.ts

@@ -7,6 +7,6 @@ export interface ExSocketInterface extends Socket {
     webRtcRoomId: string;
     userId: string;
     name: string;
-    frame: string;
+    character: string;
     position: PointInterface;
-}
+}