implemented editing of document in GUI + respective handlers in backend

frontend/src/Components/MultilineEditor.svelte

@@ -1,14 +1,16 @@
 <script>
     import { activeField } from './field_sync.svelte.js';
 
-    let { editable = false, value = $bindable(null) } = $props();
+    let { editable = false, value = $bindable(null), onSet = (newVal) => {} } = $props();
     let editing = $state(false);
 
     let editValue = $state(value);
 
     let timer = null;
-    function applyEdit(){
-        value = editValue;
+
+    async function applyEdit(){
+        let success = await onSet(editValue);
+        if (success) value = editValue;
         editing = false;
     }
 
@@ -39,7 +41,7 @@
         min-width: 40px;
         min-height: 20px;
     }
-    div:hover{
+    div.editable:hover{
         border: 1px dotted;
     }
 </style>
@@ -47,7 +49,7 @@
 {#if editable && editing}
 <textarea bind:value={editValue} onkeyup={typed} autofocus></textarea>
 {:else}
-<div onclick={startEdit}>
+<div onclick={startEdit} class={{editable}}>
     {#each value.split("\n") as line}
     {line}<br/>
     {/each}