ENH: Respect sort and limit arguments

[GuySartorelli]

These parameters are defined in the PHPDocs for Report and are technically part of the method signature. They should be respected and in the case of the new default limit in silverstripe/silverstripe-reports#139 this could have performance ramifications for large datasets.

Note that filterByCallback applies the limit from the DataList

[emteknetnz]

Seems reasonable

You'll also need to update the docblocks to include the new params

[GuySartorelli]

Updated dockblocks and fixed the $sort null check.

[GuySartorelli]

Fixed the test. The old code was calling sort but not actually using the resultant sorted list - so the test was asserting that an incorrect order was correct.
Not sure why the code wants to sort by parent ID in the first place though, tbf - @emteknetnz should I just revert the test back and remove the sort by ParentID line?

[emteknetnz]

We should keep the default sort of ParentID so that it matches how it previously behaved

[GuySartorelli]

We should keep the default sort of ParentID so that it matches how it previously behaved

In that case we should remove that sort, because the previous behaviour wasn't actually sorting. Sort was called on the list but that returns a sorted list - it doesn't sort the list in place. And the sorted list wasn't used in the old code. So the actual list used for the report wasn't sorted.
I think? I could be missing something there.

[emteknetnz]

Oh right, yes good point $records->sort("ParentID"); does nothing. Yes remove $sort = 'ParentID';

[GuySartorelli]

Removed the default sort, as it was a departure from the existing behaviour.