Fix bugs to make plugins work better in Laravel 8.x environment

Make unique index name of migrate scripts for PostgreSQL

Bug fixes for the install script
Improve Travis CI test

1. Install laravel ui:auth by default for the new project (only support Laravel >= 6.0)
2. Allow enter database username/password via install command: php artisan laravelcms
3. Automatically add a default admin user for the new project, username: [email protected] password: admin321
4. Tested in php 8 & laravel 8

Test Laravel 8.x
Add login CSS file for new cms website login/register page
Change route / to cms if it is a new website
Update steps for set up a brand new CMS website with the latest Laravel

1. Support Laravel 7
2. Added some language files
3. Tested in PHP 7.1, 7.2, 7.3, 7.4

1. Add inquiry_verify_str for basic spam check
2. Display order by sort_value for search result
3. Pass variables to the plugin for the create() method

1. Use your own PHP controller/class by adding it into a CMS page. Details: https://www.laravelcms.tech/Laravel-Advanced-Override-the-page-content-by-your-PHP-Class-method-function.html
2. The All Pages in the backend will use ReactJS by default. Details: https://www.laravelcms.tech/Laravel-Backend-All-Pages-search-and-display-settings.html
3. Frontend search improve: Allow search keyword & tag together
4. Frontend inquiry form improve: Show inquiry form even no record in the database

Add: Basic tags for a page
Add: Upgrade CMS online via browser