Improve generalisation of address types, field names and css classes

Problem/Motivation

Currently the module has the following issues:

• The address field must be called "address"
• Some of the JS and CSS is reliant on specific classes being present
• Some of the fields (i.e. State/Province) are not auto-populated as they should be.
• Address support is mainly for US or countries with states/provinces.

Proposed resolution

• To improve the code to be less reliant on specific css class and field names.
• To improve international address support.
• Some general code tidy-up.

Remaining tasks

None specific to these general updates.