New lightmode and darkmode themes with UI revamp.

Signed-off-by: Adam Treat <treat.adam@gmail.com>

gpt4all-chat/qml/MyTextArea.qml

@@ -0,0 +1,22 @@
+import QtCore
+import QtQuick
+import QtQuick.Controls
+import QtQuick.Controls.Basic
+
+TextArea {
+    id: myTextArea
+    color: enabled ? theme.textColor : theme.mutedTextColor
+    placeholderTextColor: theme.mutedTextColor
+    font.pixelSize: theme.fontSizeLarge
+    background: Rectangle {
+        implicitWidth: 150
+        color: theme.controlBackground
+        border.width: 1
+        border.color: theme.controlBorder
+        radius: 10
+    }
+    padding: 10
+    wrapMode: TextArea.Wrap
+
+    ToolTip.delay: Qt.styleHints.mousePressAndHoldInterval
+}