Improve configuration and initialization

Currently the library initializes itself - without the need to call `ko.validation.init`. Also, binding handles like `value`, `textInput` etc. are automatically wrapped to become validatable. This adds difficulties in working with libraries like [knockout-es5](https://github.com/SteveSanderson/knockout-es5) or to prevent the registration. Furthermore, some may already define extenders which this library registers. Ideally, changes to this feature should not cause any breaking changes.

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Related issues:
#477 Opt-out option for makeBindingHandlerValidatable
#478 Calling ko.validation.group on object makes all observables validatable
#404 RegisterExtenders invoked before Init, cannot avoid adding rules to ko.extends
#150 Exposing default options
#192 Add option `asyncOnModified` (Related issue #180)

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More investigation is needed for the following issues:
#540 Support live option for observable objects
#49 Changing validation rules on the fly

Start with the ko.validation.init entry point and the automatic wrapping of value and textInput binding handlers, then inspect how extenders are registered before initialization. Review related issues #477, #478, #404, #150, and #192 for existing requirements. Done should provide configurable initialization and registration behavior without breaking existing usage.

Written by the indexing model from the issue text.