Move config/address.c to address library

[flatcap]

The config code lives in the config/ directory.
It is fairly self-contained; it only relies on helper functions from libmutt.

Except for two things: Config Cache, Address Type.

The architecture of the Config System should allow us to define types without needing the code to live in the config/ directory.
Move the Address Type functions into the address/ directory.

• config/address.[ch]
• Helper function from config/helpers.[ch]

This will remove libconfig's dependency on libaddress.

This is a simple job to adjust the Makefile, but there's slightly more to do, to connect everything up.

If you like puzzles, I'll leave it at that.
(or I can provide a list)

[roccoblues]

started here: #3992

[flatcap]

Completed in: f9d941e