Change directory/app structure, add Composer, routes, PDO DB connections, models (DB), index.php for bootstrapping, file validation test

The directory/application strucutre has been modified to better organize all the files. All files that have to do with the application should go under the app/ folder. This includes any custom classes, HTML, models (databases)...everything that's not a third-party/external library/dependency. Now we need to refactor everything to fit this structure and get rid of the files in the root directory.

Composer has been added to handle dependency management and autoloading of the application classes. It can be installed from https://getcomposer.org/download/. The composer.json file manages eveverything that has to do with Composer. If a new folder is added and contains classes, it should be added to the autoload -> classmap in the JSON file. The commands you need to use Composer are:
	- 'composer install' 	   - run this command if you add a new dependency/package to the JSON file
	- 'composer update'  	   - updates the currently installed packages/dependencies
	- 'composer dump-autoload' - creates a new autoloading file; this needs to be run if a new class or folder (with classes) is added

Routes haven't quite been implemented yet, but the basic idea is they all go inside the file 'routes.php' inside the 'config' folder. Routes are all the accessible URL/URIs in our app. Instead of accessing actual PHP files, users will instead go to URIs that the router will handle. For example, we could have a route '/foo' and to access it, a user would go to 'http://fhsapp.com/foo', our app will receive the request, check whether it exists, and call the specified function for the route and pass any parameters or aguments as necessary. This may be confusing right now, but it'll be straightforward and easy to understand once we get this fully implemented.

PDO has been implemented for accessing the database and we should always use it from here on out. As the application is refactored, we should only be using models (explained below) to communicate with the database. If we need to perform a raw SQL query, we will still use PDO. If you need to know more about this, read the docs at 'http://php.net/manual/en/book.pdo.php'.

All communication with the database should now happen through models. Essentially, models can be thought of as database tables. Each table has (a) model(s) associated with it and methods to access the database. The model (class) name should be SINGULAR and the associated table will have the model's name in snake case. For example, the model 'UserOrders' would have the table 'user_orders'. Of course, we can override the table name by defining '$this->tableName = 'tableName';' in the child constructor. All models should extend the Model class. With models, we can access information from the database using methods such as 'find(id)', 'all', 'findBy(attribute, value)', etc...

Instead of directly accessing files, we'll be using a bootstrapping process to direct users to the right page. The bootstrapping process will use the routes to handle user requests. All requests go to index.php in the 'public' folders.

A file validation test has been added using the PHPUnit framework. To use PHPUnit, you can install it from 'https://phpunit.de/getting-started.html'. The included files for testing are included the assets folder in the tests directory.