MDL-27547 When deleting a local plugin containing a built-in service, the built-in service is not deleted

Revert "MDL-30843 and MDL-30842 - accessibility compliance: Add <label> for form input text and select tag"

This reverts commit f9f281b8.

determine if the 'id' column is sequence based or no

MDL-32323 make base test case classes abstract to prevent empty testcase warnings, fix property access

This should help with compatibility of future PHPUnit and it also allows us to improve test reset without breaking existing moodle test cases.

1/ type/match/tests/walkthrough_test.php - tests are failing randomly, looks like some weird randomisation is going on there - see TODOs

2/ type/multianswer/tests/upgradelibnewqe_test.php contains invalid expected value - see TODO

Random users now get proper first and last names, course and category descriptions contains longer text. The names can be also used as source of random complex utf-8 strings.