Fix white spaces in schema field name that block saving without feedback

Defining a schema field in Studio, when I enter a white space in the field name :

• there's no red feedback saying it's forbidden
• save does nothing nor says it doesn't
• leaving the page displays the "save, discard, cancel popup", when save is pressed the page is changed but the save is not done and current work is lost

The problem is present on connect.nuxeo.com

TODO

• Check with core team what should be accepted in this field

AC

• When a schema field contains an invalid character, display a validation error mentioning:

  Field [field name] contains invalid characters. Accepted values are [valid values, e.g. alphanumerical characters, dashes (-) and underscores (_)].

• Error message display does not lead to a XSS.
• When a schema field contains an invalid character, visually show which field(s) containing invalid data.
• When invalid characters are removed, remove mentions of the error.