Fix inconsistent hooks: Model.php & SQL/Model.php

Going on from pull request **"added missing hooks #484"**

I dug a little deeper - and as you say the hooks weren't missing but are in fact named inconsistently between the two classes...

Hooks in Model.php were: "beforeUpdate" & "afterUpdate" (See links below)
Hooks in SQL/Model.php were: "beforeModify" & "afterModify" (Again,
links below)

The names of the hooks in Model.php make more sense (at least to me)
and when used in SQL follow with the UPDATE statement that is generated.
Therefore I have changed the names of the hooks in SQL/Model.php to match
those in Model.php

https://github.com/atk4/atk4/blob/7b97da192658af4b08e34039106984f31a248265/lib/Model.php#L360
https://github.com/atk4/atk4/blob/7b97da192658af4b08e34039106984f31a248265/lib/Model.php#L368

https://github.com/atk4/atk4/blob/7b97da192658af4b08e34039106984f31a248265/lib/SQL/Model.php#L678
https://github.com/atk4/atk4/blob/7b97da192658af4b08e34039106984f31a248265/lib/SQL/Model.php#L685