Send party venue field through as a distinct field to Wordpress

[ngm]

In relation to issue #181, we need to send through the new party venue field as a distinct field to Wordpress. Then the party location can simply be sent through as the location, and the check for the presence of a value in the venue field to determine what goes in to the location field can be removed.

Then, in the front-end, we will have access to both venue and location, and this will allow us to implement #181.

[ngm]

@NikhitaPaturu could you have an investigate into how to add a new custom field to the Party entity in Wordpress?