CAKE-20 | updated exchange and exchange template pages; created exchange_view_model and applied to exchange and exchange template pages; applied new design to menu widget; changed text validator and amount validator

lib/src/widgets/base_text_form_field.dart

@@ -72,6 +72,10 @@ class BaseTextFormField extends StatelessWidget {
               borderSide: BorderSide(
                   color: borderColor ?? Theme.of(context).dividerColor,
                   width: 1.0)),
+          disabledBorder: UnderlineInputBorder(
+              borderSide: BorderSide(
+                  color: borderColor ?? Theme.of(context).dividerColor,
+                  width: 1.0)),
           enabledBorder: UnderlineInputBorder(
               borderSide: BorderSide(
                   color: borderColor ?? Theme.of(context).dividerColor,

lib/src/widgets/nav_bar.dart

@@ -71,6 +71,8 @@ class NavBar extends StatelessWidget implements ObstructingPreferredSizeWidget {
           EdgeInsetsDirectional.only(bottom: _paddingBottom, top: paddingTop),
       child: CupertinoNavigationBar(
         leading: leading,
+        automaticallyImplyLeading: false,
+        automaticallyImplyMiddle: false,
         middle: middle,
         trailing: trailing,
         backgroundColor: backgroundColor,

lib/src/widgets/trail_button.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:cake_wallet/palette.dart';
 
 class TrailButton extends StatelessWidget {
   TrailButton({
@@ -21,7 +22,7 @@ class TrailButton extends StatelessWidget {
         child: Text(
           caption,
           style: TextStyle(
-            color: Theme.of(context).primaryTextTheme.caption.color,
+            color: PaletteDark.lightBlueGrey,
             fontWeight: FontWeight.w500,
             fontSize: 14),
         ),