Rename view models

We don't need a cell specific view model. It seems like it's more useful
to have a view model that represents a specific user. That way we can do
any transformations we need to do in one place. This essentially turns
the view model into a facade for use in displaying the model.

To reduce confusion, I'm also renaming EmployeesViewModel to
EmployeeListViewModel, which is actually a little more accurate about
what it's modeling.
Add detail screen

- Basic design of the detail screen
- Add properties to EmployeeViewModel to handle the additional info
  required for the detail screen
Handle optionals a bit better

By using `fmap` and `apply`, we can handle the case of missing fields a
bit better and prevent quite a few crashes.
Update CocoaPods
Update implementation of apply in terms of fmap
Ignore the error coming back from the API client

We aren't using this. It shouldn't have been named in the first place.
Small style fixes