rename adapters with new file structure

[jacobmerson]

With the new file structure we should rename the adapters so that they have consistent naming within the folder.

So, including adapters will look like:

#include <pcms/adapter/omega_h/layout.h>
#include <pcms/adapter/omega_h/field.h>
#include <pcms/adapter/vmec/layout.h>
#include <pcms/adapter/vmec/field.h>