Add Ormin ORM support for BaraDB (Nim client)

clients/nim/ormin/examples/chat/frontend.nim

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+## Frontend for our chat application example.
+## You need to have 'karax' installed in order for this to work.
+
+import karax / [kbase, karax, vdom, karaxdsl, kajax, jwebsockets, jjson,
+                jstrutils, errors]
+
+# Custom UI element with input validation:
+
+proc validateNotEmpty(field: kstring): proc () =
+  result = proc () =
+    let x = getVNodeById(field)
+    if x.text.isNil or x.text == "":
+      setError(field, field & " must not be empty")
+    else:
+      setError(field, "")
+
+proc loginField(desc, field, class: kstring;
+                validator: proc (field: kstring): proc ()): VNode =
+  result = buildHtml(tdiv):
+    label(`for` = field):
+      text desc
+    input(`type` = class, id = field, onchange = validator(field))
+
+# here we setup the connection to the server:
+let conn = newWebSocket("ws://localhost:8080", "orminchat")
+
+proc send(msg: JsonNode) =
+  # The Ormin "protocol" requires us to have 'send' implementation.
+  conn.send(toJson(msg))
+
+type User* = ref object
+  name*, password: kstring
+
+const
+  username = kstring"username"
+  password = kstring"password"
+  message = kstring"message"
+
+# Include the 'chatclient' helper that Ormin produced for us:
+include chatclient
+
+template loggedIn(): bool = userId > 0
+
+proc doLogin() =
+  registerUser(User(name: getVNodeById(username).text,
+                password: getVNodeById(password).text))
+
+proc doSendMessage() =
+  let inputField = getVNodeById(message)
+  sendMessage(TextMessage(author: userId, content: inputField.text))
+  inputField.setInputText ""
+
+proc registerOnUpdate() =
+  conn.onmessage =
+    proc (e: MessageEvent) =
+      let msg = fromJson[JsonNode](e.data)
+      # 'recvMsg' was generated for us:
+      recvMsg(msg)
+      karax.redraw()
+
+proc main(): VNode =
+  result = buildHtml(tdiv):
+    tdiv:
+      if not loggedIn:
+        loginField("Name :", username, "input", validateNotEmpty)
+        loginField("Password: ", password, "password", validateNotEmpty)
+        button(onclick = doLogin, disabled = disableOnError()):
+          text "Login"
+        p:
+          text getError(username)
+        p:
+          text getError(password)
+    tdiv:
+      table:
+        for m in allMessages:
+          tr:
+            td:
+              bold:
+                text m.name
+            td:
+              text m.content
+    tdiv:
+      if loggedIn:
+        label(`for` = message):
+          text "Message: "
+        input(class = "input", id = message, onkeyupenter = doSendMessage)
+
+registerOnUpdate()
+runLater proc() =
+  getRecentMessages()
+
+setRenderer(main)