build: Add folks-internal.la to $(backend_libadd)
eds: Remove unused -include in Makefile.am
dummy: Modernise build system
dummy: Fix documentation in dummy-backend-factory.vala
dummy: Add missing -uninstalled.pc.in pkg-config template
dummy: Fix copyright header
dummy: Fix nullability of a type in the persona store
dummy: Fix some documentation comments
dummy: Validate the types of personas exposed by the persona store
dummy: Reformat some code

No functional changes.
tests: Remove unused variables from Makefile.ams
tests: Add missing valgrind.mk include to test Makefile.ams
fixup! dummy: Validate the types of personas exposed by the persona store
tests: Tidy up dummy tests Makefile.am
dummy: Partially fix g-ir-scanner namespace issues
dummy: Rename backend library namespace from Dummyf to FolksDummy

This fixes an un-work-round-able problem with g-ir-scanner whereby
subclassing (e.g. FatPersona: Persona) within the library broke node lookup
in g-ir-scanner due to mismatching namespaces.

It’s also a much more recognisable name.
dummy: Fix coding style
dummy: Refactor individual-retrieval test

Reduce code duplication by a huge amount. Obscure the personal details of
one of the developers.
dummy: Don’t use deprecated API in unit tests
dummy: Remove an unnecessary idle callback from the individual-retrieval test