Split assertions in traits, update codebase

[TavoNiievez]

• Removed compatibility logic for unsupported versions of Symfony.
• Encapsulated access to services.
• PHP 7.3 features applied.
• Removed event compatibility logic for Laravel < 5.4.
• The connector methods used by the module are now at the end of the class in an adjoining block.
• Removed unnecessary type hints docblocks.
• Added more typing to functions.
• Improved IDE help when browsing the module source code.
• Now assertSame is used instead of assertEquals.
• Fixed broken links to laravel documentation.

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• Module assertions are now organized into traits based on their related functionality and following the Laravel naming convention:
  

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• Added amActingAs, assertAuthenticatedAs, assertCredentials, assertInvalidCredentials, authentication assertions.
• Added seedDatabase function.
• Added enableMiddleware function.
• dontSeeRecord and seeRecord functions now works with Model objects too.
• disableMiddleware function now can disable one or more specific middleware by specifying the $middleware parameter.

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Note: This PR will be merged with the Rebase and merge strategy.