Add simple phpunit tests

[Raruto]

I have created some really simple tests for the Forms module (hoping this can serve as a starting point for other critical parts as well...)

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List of changes:

• add .gitattributes files in order to exclude tests folder from releases
• remove tests folder from .gitignore files
• require phpunit ^7 as composer.json dev dependecy
• add phpunit.xml.dist and tests/bootstrap.php autoloader
• add tests/modules/FormsTest.php test file

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Useful links:

• piotr-cz/cockpit-sql-driver for sample database tests
• PHPMailer/PHPMailer for sample email tests
• Getting started with PHPUnit 7
• PHPUnit Manual

Happy Testing,
Raruto