Add Model::deleteAll and Model::forceDeleteAll

[luisscruza]

What do you think of adding a Model::deleteAll and Model::forceDeleteAll method to the Model?

Right now, we can do Model::query()->truncate(); to delete all records from a table, but this also resets the identity order of the table.

It can be useful to just do Model::deleteAll and keep the same identity going on the new created records.

Should this be worth a PR?

[noefleury]

Using Model::query()->delete() or Model::query()->forceDelete() should work as expected.