enhance client endpoints, tweaks for data consistency

[ajohnson052]

This PR accomplishes several things:

Issue #17 - tests and error handling for clients endpoints

• moved render_errors and render_not_found up to the API Controller
• validations for the client class, to further enhance error handling

Issue #80 - counties should be restricted

• this is handled with a model level validation
• on the front end, the dropdown still hold the full name but submits the abbreviation

Cleanup

• previously we were not handling time zones very consistently, and some tests would occasionally fail because of it
• after peaking with @pollygee about business requirements, it was established that we can focus on associating appointments with dates and not times for MVP

[pollygee]

@ajohnson052 looks great!

My only question is that in going through creating an appointment, it looks like you can manually type information in and save an appointment. We never get an error for that but the apmt isn't saved you have to go create an client on the other tab then come back and make an appointment. Maybe this should be another ticket though and we can merge this and I'll create another ticket? What do you think?

I'm thinking that the rest of the boxes should be greyed out and not be selectable or invisible until you select a client...that way it's not confusing for non-tech people. Alternatively and maybe easier for MVP we can just flash an error message that the client doesn't exist, need to create the client before you can make an appointment for them.

Let me know what you think! Thanks for all the great work!

[ajohnson052]

@pollygee - you're right, we definitely need to address the appointment creation flow, but I wasn't considering that as part of this issue.

I just created issue #96 as a placeholder for the appointment creation flow, but it still needs the description filled out