Add client side validation for adding service areas

[Mike-Heneghan]

Currently, some users are adding service areas which are already encompassed for example adding Scotland and then regional service areas.

It would be relatively easy to add simple client-side validation to nudge users to either use regional service areas or national ones but not both.

[Mike-Heneghan]

Made slightly more complex as the Service Area field is abstracted out. Due to the complexity of trying to update the generic field and mutli-select might be better to start by creating a service-area specific code to make it a bit more explicit then optimise later.

[Mike-Heneghan]

Placeholder Message to avoid resizing:

Once the area is clicked on a message appears to select either national or regional:

If only national is selected then regional options are hidden:

If regional option are selected then national are hidden:

[Mike-Heneghan]

Merged into master