Apps: divide the modules in direct command modules, support library and init

Most modules are direct implementations of openssl application
sub-commands, but some constitute a support library, which can be used
by more than one program (and is, incidently, by test/uitest).

For practical purposes, we place the support library modules in a
private, static library.

Finally, there are some modules that don't have direct references in
the rest of the apps code, but are still crucial.  See them as some
kind of extra crt0 or similar for your platform.

Inspiration from David von Oheimb

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5222)