NEW AdminController as superclass for /admin/* routed controllers #1638

Job	Run time
CI / Generate matrix	14s
CI / Context	1s
CI / 8.3 prf-low mariadb phpunit all	1m 51s
CI / Check governance	0s
CI / 8.3 mysql80 phpunit all	1m 16s
CI / 8.3 mysql80 phplinting	1m 46s
CI / 8.3 mysql80 endtoend root job1	2m 38s
CI / 8.3 mysql80 endtoend root job2	2m 38s
CI / 8.3 mysql80 endtoend root job3	2m 36s
CI / 8.3 mysql80 js	1m 17s
CI / Dispatch tag patch release	0s
	14m 17s

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