Add 'write' access for post FSE

+ hasMessageConfAndAreaWrite()
+ MenuModule helpers: gotoMenuOrPrev(), gotoMenuOrShowMessage(). These will likely replace many other pieces of code soon.

core/msg_area_post_fse.js

@@ -4,6 +4,9 @@
 const FullScreenEditorModule    = require('./fse.js').FullScreenEditorModule;
 const persistMessage            = require('./message_area.js').persistMessage;
 const UserProps                 = require('./user_property.js');
+const {
+    hasMessageConfAndAreaWrite,
+}                               = require('./message_area.js');
 
 const _                         = require('lodash');
 const async                     = require('async');
@@ -59,12 +62,25 @@ exports.getModule = class AreaPostFSEModule extends FullScreenEditorModule {
     }
 
     enter() {
-        if(_.isString(this.client.user.properties[UserProps.MessageAreaTag]) &&
-            !_.isString(this.messageAreaTag))
-        {
-            this.messageAreaTag = this.client.user.properties[UserProps.MessageAreaTag];
-        }
+        this.messageAreaTag =
+            this.messageAreaTag ||
+            this.client.user.getProperty(UserProps.MessageAreaTag);
 
         super.enter();
     }
+
+    initSequence() {
+        if(!hasMessageConfAndAreaWrite(this.client, this.messageAreaTag)) {
+            const noAcsMenu =
+                this.menuConfig.config.messageBasePostMessageNoAccess ||
+                'messageBasePostMessageNoAccess';
+
+            return this.gotoMenuOrShowMessage(
+                noAcsMenu,
+                'You do not have the proper access to post here!',
+            );
+        }
+
+        super.initSequence();
+    }
 };