Remove datepicker if readonly is active

[stefanheimes]

We should change the getFieldDefinition. If the "readonly" is active we don't need the Datepicker. Because the datepicker is able to set a new Date.

    public function getFieldDefinition($arrOverrides = array())
    {
        $strDateType                 = $this->getDateTimeType();
        $readOnly                    = $this->getOverrideValue('readonly', $arrOverrides);
        $arrFieldDef                 = parent::getFieldDefinition($arrOverrides);
        $arrFieldDef['eval']['rgxp'] = $strDateType;
        if (!$readOnly) {
            $arrFieldDef['eval']['datepicker'] = ($strDateType !== 'time');
        }

        return $arrFieldDef;
    }

[discordier]

Looks good to me. Do it.

[zonky2]

pls look at #21