Add strict type coding standard (aces#6039)

Previous attempts to force type hints or strict typing en masse have failed because it's just too darn complicated to do it all at once.

This introduces a new Strict Type coding standard that we can selectively apply to files by adding to an array in test/run-php-linter.sh. Hopefully this will provide an approach to using stricter typing that is easier to author and review.

Using vendor/bin/phpcbf --standard=test/StrictTypesCS.xml $file will now allow PHPCBF to automatically provide

    return types
    param types
    strict_types =1

based on PHPDocs.

It will also throw errors if Traversable types do not have specific type annotations.

The Database.class.inc file has been modified as an example of the changes

Resolves aces#5342

composer.json

@@ -20,7 +20,8 @@
         "php-webdriver/webdriver" : "^1.8.2",
         "phan/phan": "^2.4",
         "phpmd/phpmd": "~2.8",
-        "phpstan/phpstan": "0.12.17"
+        "phpstan/phpstan": "0.12.17",
+        "slevomat/coding-standard": "^6.0"
     },
     "scripts": {
       "pre-install-cmd": "mkdir -p project/libraries"