Enhance Field Validation integration using remote validation

Problem/Motivation

Currently the Field Validation (field_validation) integration is by default limited to those validations known to clientside_validation_field_validation_regular().
This is great since those validations ensure that whatever can be done on the client side is done there.
However it would be nice to be able to run more complex validations using the remote validation functionality that's shipped with jQuery.validate.
There already examples for "remote" validations e.g. drupalURL / phone / captcha. Although those validations use synchronous (blocking) ajax calls which can lead to bad user experience.

Proposed resolution

The attached patch contains:

• Generic remote validation integration for any Field Validation rule.
  
  If a rule can't be re-created on the client side the validation method fieldValidationAjax is used - all Field Validation rules are collected and executed at once.
  The ajax callback is done using jQuery.validator.methods.remote(), this ensures maximum compatibility with jQuery.validator and is a non-blocking (async) approach. Further this ensures we'll have context specific error messages.
  The integration is as generic as possible, however further testing is needed to see if there are any uncovered scenarios.
• Generic integration with High-performance JavaScript callback handler. The code does it's best to handle dependencies to be able use the JS callback.
• Enhanced the ajax handling for the remote validation. Supports now progress (throbber) and works around some quircks with the success handler of jquery.validation
• Integration with Drupal.states.Trigger.states, which means you can now use #states to write something like this:
  

  $form['email_retype'] = array(
      '#type' => 'textfield',
      '#states' => array(
        // Hide the email re-type field as long as the email field hasn't valid data.
        'invisible' => array(
         ':input[name="email"]' => array('clientside_validation' => FALSE),
        ),
      ),
    );
  

  This is globally available and independent from "Field Validation". Available states are:

  • clientside_validation (!clientside_validation): TRUE on initialization. Set once the validation is run
  • clientside_validated (!clientside_validated): FALSE on initialization. TRUE if the validation is done, reset to FALSE as soon as the value is changed.
• Integrate with Conditional Fields - which means you can now configure the #states in the Field UI!

Remaining tasks

Reviews needed.

User interface changes

None.

API changes

If someone already uses hook_clientside_validation_rule_alter() the new implementation might duplicate or interfere with that custom validation.