Standard New and Edit functionality

public with sharing class ReadingPermissionController {

    public ReadingPermission__c newReadingPermission {get;set;}
    public String returnUrl {get;set;}
    
    public ReadingPermissionController(ApexPages.StandardController setCon) {
        ReadingPermission__c r = (ReadingPermission__c) setCon.getRecord(); 
        newReadingPermission = new ReadingPermission__c();
        if(r.Id != null) {
            newReadingPermission = [Select Id, Name, Permission_Holder_Name__c, Permission_Holder_ID__c, Permission_Holder_Type__c, Granted_Permissions__c from ReadingPermission__c where id =: r.Id];   
        }
        //system.assert(false, newReadingPermission );  
        returnUrl = apexpages.currentPage().getParameters().get('retURL');
    }
    
    public List getReviewerList() {
        List options = new List();
        options.add(new SelectOption('' , '--None--'));
        List users = [Select Id, name from user where profileId in: OnlineReadingBaseClass.getOnlineReadingProfileIds()];
        for(User u : users) {
            options.add(new SelectOption(u.Id, u.Name));
        }
        return options;
    }
    
    public List getQueueList() {
        List sOptions = new List();
        List groupList = [select Id, name from Group where type = 'Queue'];
        sOptions.add(new SelectOption('' , '--None--'));
        for(Group g : groupList) {
            sOptions.add(new SelectOption(g.Id , g.Name));
        }
        return sOptions;
    }
    
    public List getGroupList() {
        List sOptions = new List();
        List groupList = [select Id, name from Group where type = 'Regular'];
        sOptions.add(new SelectOption('' , '--None--'));
        for(Group g : groupList) {
            sOptions.add(new SelectOption(g.Id , g.Name));
        }
        return sOptions;
    }
    
    public PageReference save() {
        PageReference pag = null;
        try {            
            upsert newReadingPermission;
            pag = new PageReference(returnUrl);
        } catch(Exception e) {
            ApexPages.addMessages(e);
        }
        return pag;
    }
    
    public PageReference saveAndNew() {
        PageReference pag = null;
        try {            
            upsert newReadingPermission;
            newReadingPermission = new ReadingPermission__c();
        } catch(Exception e) {
            ApexPages.addMessages(e);
        }
        return pag;
    }
    
    public PageReference cancel() {
        return new PageReference(returnUrl);
    }
}

      
      
       #loading-image {
            position: fixed;
            top: 40%;
            left: 40%;
        }
    
       #loading {
            width: 100%;
            height: 100%;
            top: 0px;
            left: 0px;
            position: absolute;
            display: none;
            opacity: 0.5;
            filter: alpha(opacity = 50);
            -moz-opacity: 0.5;
            background-color: #fff;
            text-align: center;
            z-index: 100;
        }
      
      
      
        //function for showing loading image
        function showLoadingImage() {
            document.getElementById('loading').style.display='block';
        }
        
        
        //function for hiding loading image
        function hideLoadingImage() {
            document.getElementById('loading').style.display='none';
        }