Suggestion: `loadFixtures()`: Change the default for `append` to false

The default mode when loading fixtures is to **purge**: https://symfony.com/bundles/DoctrineFixturesBundle/current/index.html#loading-fixtures

> By default the `load` command purges the database

But with `$I->loadFixtures()`, the default is to **append**. I think this is confusing and should be changed. However, I don't see any easy upgrade path... ;-)