Add support for explicit field ordering

This PR basically updates jquery.addressfield for the 1.x config schema of [addressfield.json](https://github.com/tableau-mkt/addressfield.json).  The changes required to support this were surprisingly simple.

#### API Additions
- Introducing the `$.fn.addressfield.onlyKey()` helper method.  Useful for getting field names from addressfield.json field objects, as well as option object values.
- Introducing the `$.fn.addressfield.hasField()` method. Used to determine if a given configuration contains a given field.

#### Backwards incompatible API Changes
Other than the whole configuration schema change... Updates in existing implementations would have to be made to:
- The expected format of the argument provided to `$.fn.addressfield.updateOptions()` has changed to match the new configuration schema in addressfield.json 1.x, e.g.:
```json
[
  {"AA" : "AA Value"}, 
  {"BB" : "BB Value"}
]
```