Header file directory mismatch between source and installation

[Fuad-HH]

This line is changed here to move the omega_h_field.h to the adapter subdirectory.
https://github.com/SCOREC/pcms/blame/bcb4fc45c6304ce33f603b94a336a8f81a239dc7/src/pcms.h#L6

But when the pcms.h header is included in an external project, it cannot find this adapter directory. I think it's because the adapter directory is not created during the installation.

@jacobmerson, @hgangwar

[jacobmerson]

Harsh and I discussed this and we have decided that there will be removing the pcms.h header. This will provide more direct control over what the user is bringing in. He is also updating the installation to make sure all of the adapters are installed int he appropriate folder.

[jacobmerson]

This is handled in #260