closes #434, #408 - added $event to onValidationError

[zoul0813]

added $event to onValidationError and call preventDefault when onValidateBeforeSubmit is true

We can't prevent the submit after waiting for async validation, so we just prevent it before calling any validation and let the user
manually submit the form in the onSubmit handler, if it validates.

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Bug Fix

• What is the current behavior? (You can also link to an open issue here)
  <form /> are submitted when using submit field with validateBeforeSubmit.

• What is the new behavior (if this is a feature change)?
  validateBeforeSubmit: true calls $event.preventDefault() and prevents the form submission

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  This PR should introduce "expected behavior", so users should not need to do anything.

• Other information:

[zoul0813]

@icebob I'm going to merge this in later today as no one else has reviewed it. OK?

Also - if I bump the version that will automatically do an npmjs update?

[icebob]

OK.

Yes, but you have to use npm run version .... script. More info: #246 (comment)

[zoul0813]

@icebob yes, I'm going to do that a separate PR with the version bump and include refs to the issues included in it. Thanks.