These libraries are bound for E-D-S so they live at the lowest layer of
Evolution for now -- even libeutil can link to them (but please don't).
This is the first step toward moving mail handing to a D-Bus service.
We have a confusing array of nearly-identical CFLAGS/LIBS definitions in
configure.ac. Time to simplify. Instead let's just have one definition
that includes all the libraries provided by Evolution-Data-Server (incl.
Camel). That, in combination with GNOME_PLATFORM, gives us most of what
we need for compliation and linking, and we can sprinkle definitions for
additional library dependencies in Makefile.am's as needed.
The settings library started using an EMailBackend object, but since
it is abstract it can't be instantiated directly. So we use the EShell
to get the mail backend for us instead, after loading the modules.
