New quick easy access to health tool from site administration block

Having a quick, easy access to health tool from site administration block would allow moodle admins worldwide to check their database for basic errors and see suggested fixes.

Even though the health tool is very user friendly, the user must know its existence and how to invoke it via web. If it were made accessible within the site administration block (in server) it would be used more often and more sites would have fewer errors.

Also, if the server kept track of its usage, it might suggest administrators to run it (every n days), just as the cron job is handled now.