Adding a new function `dateToTimeZone` to AbstractBuilder

The function convert a a string into a proper date object, whith the specified timeZone for the builder.
By default, its GMT+2 (Europe/Paris) time.

This is justified by the fact that the timeZone is not usually saved in DB so we need to specify a default one
\Datetime
\DateTimeZone
Ok, c'est juste une best practice, ça évite les risques de collisions