Add Config flag for max returned rows

See https://github.com/nadavkav/moodle-block_configurablereports/commit/181b56df5372000e2d7d42900cb720be70c8b328 and next pull request
Add config option to settings.php

Also see next merge request
Last pull request max rows
Merge pull request #18 from DBezemer/patch-1

Add Config flag for max returned rows
Merge pull request #20 from DBezemer/patch-3

Last pull request max rows
Merge pull request #19 from DBezemer/patch-2

Add config option to settings.php