Validation messages should be set in the form options

[iGormilhit]

Describe the issue
validationMessage that are not described in the form options but in the JSON schema won't be displayed in the editor. This behaviour changed from json-schema-form to angular6-jsonschema-form library.
⚠️ Please check all schemas and form options.

To Reproduce
Steps to reproduce the behavior:

1. As a librarian, create or edit a patron.
2. In the phone field, hit the a key (for example).
3. See the error validation message which is the pattern.
4. Compare to https://github.com/rero/rero-ils/blob/master/rero_ils/modules/patrons/jsonschemas/patrons/patron-v0.0.1.json#L82

Expected behavior
The validation message should be displayed. In order to do that, add the following in the patron form options:

"validationMessage": {
    "pattern": "Phone number with the international prefix, without spaces, ie +41221234567."
}

Software version
ils.test.rero.ch, v0.5.1

ilsdev.test.rero.ch, 9aa529c