Start to unskip datetime tests.
Fix up some limits that go funny when FormHelper starts using DateTime.
Start making FormHelper::dateTime() tests pass.

Split a big test up into some smaller ones that are a bit easier to work
with. Re skip some test as they are failing.
Fix selected values in some cases.

When second is missing, or when the meridian is present array values
need to be adjusted.
Remove dateFormat and timeFormat arguments from dateTime()

These arguments are replaced with options. This makes dateTime() more
like other input methods and replaces formatting options with templates.
Rename attributes to options in datetime()

This makes it more consistent with other methods in the class.
Add assertions to ensure all select elements are present.
Merge pull request #2887 from markstory/3.0-form-datetime

3.0 formhelper datetime