Improve UI strings of admin pages

• "Token batch size." (see in code → and on l.d.o as ID#2736306 → )
• "The number of expired token to delete per batch during cron cron." (see in code → and on l.d.o as ID#2736307 → )
• "When enabled, autorized clients will be stored and a authorization requests for the same client with previously accepted scopes will automatically be accepted." (see in code → and on l.d.o as ID#2670689 → )
• "The implicit grant has the potential to be used in an insecure way. Only enable this if you understand the risks. See https://tools.ietf.org/html/rfc6819#section-4.4.2 for more information." (see in code → and on l.d.o as ID#2580240 → )

Patch will come on the next weekend.