Add field error handling.

A first approach to handling form field errors. This expects the
server to return a hash of the form:
  {
    "success": false,
    "errors": {"title": ["Enter a title, please."]}
  }
Remove some extra spaces.
Add error class to div, instead of the input itself

This tweaks the triggerValidationErrors function, and moves the error
class to the div, so we can do a little more with CSS.
Display error message, clear errors when no errors.
Merge pull request #15 from grilix/field_errors

Field errors