Implement moving on engine

Thus make all state management the engine's responsibility, and remove
the state maintaining code from frontend!

frontend/main.js

@@ -17,16 +17,13 @@ function post_json(url, json) {
 }
 
 class Backend {
-  constructor() {
-    this.config = new Configuration(
-      new Map(Object.entries(get_json("http://localhost:3000/get_state/")))
+  getConfig() {
+    return new Map(
+      Object.entries(get_json("http://localhost:3000/get_state/"))
     );
   }
-  getConfig() {
-    return this.config;
-  }
   makeMove(source, target) {
-    this.config.makeMove(source, target);
+    return post_json("http://localhost:3000/make_move/", [source, target]);
   }
   getAvailableMoves(position) {
     return post_json("http://localhost:3000/get_moves/", position);
@@ -44,7 +41,7 @@ class Chess {
     this.canMoveTo = [];
     document.onclick = (ev) => this.click(ev);
   }
-  syncBackend() {
+  updateState() {
     let config = this.backend.getConfig();
     this.configVis.configuration = config;
     this.configVis.draw(this.canvas);
@@ -63,7 +60,7 @@ class Chess {
     }
     this.activeSquares.unselectSquare(this.canvas);
     this.activeSquares.unsetMoveSquares(this.canvas);
-    this.syncBackend();
+    this.updateState();
     this.moveSource = null;
   }
   click(ev) {
@@ -82,30 +79,4 @@ class Chess {
   }
 }
 
-class Configuration {
-  constructor(board) {
-    this.board = new Map(board);
-  }
-  getAt(position) {
-    if (!this.board.has(position)) {
-      return null;
-    }
-    return this.board.get(position);
-  }
-  setAt(position, piece) {
-    this.board.set(position, piece);
-  }
-  dropAt(position) {
-    this.board.delete(position);
-  }
-  makeMove(source, target) {
-    const piece = this.getAt(source);
-    if (piece === null) return;
-    else {
-      this.setAt(target, piece);
-      this.dropAt(source);
-    }
-  }
-}
-
 new Chess();