Add time() to FormHelper.

Add concrete time input methods to FormHelper. This will let input()
also generate time type inputs.
Add date type to FormHelper.

Add a concrete method for generating date inputs and remove workarounds
in _getInput().
Reduce duplication in docs and fix typos.
Remove parameter that does nothing.
Add missing coverage for attributes with secure().
Merge pull request #2983 from markstory/3.0-form-time-type

3.0 form time type