getCMSFields: set field max length according to db fields

[Zauberfisch]

check if we can make the default getCMSFields() loop through all fields and set the max length of text fields to the max length of the DB field

<@simon_w|air> greseky, $field = $this->dbObject('Field'); if ($field instanceof Varchar) $textField->setMaxLength($field->getSize())

use case: a field of type Varchar usually has a max length of 50, which for example can result in a cut of title after saving and confusing the CMS user