[5.4] Update description of filled rule

`filled` isn't really required. It just implies that it needs a value.

Refactor npm scripts

Per #4147, this adds a new `npm run watch-poll` command, and dries up some of those long repetitive commands.

Change hard-coded '/login' param to named route

Update package.json

update laravel mix to new version

Updated axios, jQuery, Laravel Mix, Lodash and Vue.js versions

Add font path variable

Apply fixes from StyleCI

Updated laravel-mix version

Laravel 5.4 explicitly require phpunit 5.7.0+

As demonstrated in laravel/framework#17699 it is possible to have phpunit being installed with a lower than `5.7.0`, which doesn't work at all on 5.4 due to the changes with PHPUnit namespaced class.

Add App locale as default value of 'lang' attribute

Add App locate as default lang in the app.php config file instead of 'en' of 'lang' attribute in the main view.

Revert "Append '@' to let composer resolve PHP executable"

Make Axios automatically send `X-CSRF-TOKEN` in the header

Append '@' to let composer resolve PHP executable

To execute PHP scripts, you can use `@php` which will automatically resolve to whatever
php process is currently being used.

See https://getcomposer.org/doc/articles/scripts.md#executing-php-scripts
for more information.

Remove redundant check from bootstrap/autoload.php

Redundant check removed since compiled class file generation was removed
https://github.com/laravel/framework/commit/09964cc8c04674ec710af02794f774308a5c92ca#diff-7b18a52eceff5eb716c1de268e98d55dL870

Remove the hot file from versionning

Following https://github.com/laravel/framework/pull/17571, I was correctly pointed that the small proposition should be made over here. Here's a copy / past of my message, for clarity's sake.
---

When you run `npm run hmr`, a `hot` file is created to the public folder for the `mix()` helper to know if it has to server from the webpack server or not. This file does not go away until we run `npm run dev` (or `watch`). 

True, if we use `npm run production` in our production server it goes away too, but in case we don't make it go away in development, I don't think it's necessary to version it.

Ensure cross-env gets executed by node

Update composer.json to contain autoload-dev for Test namespace

Only autoload the tests namespace in dev.