lei_mirror: load most modules up-front

lei_mirror: load most modules up-front

lei lazy loads LeiMirror itself lazily, anyways, and it only
supports HTTP(S) mirrors, so there's no point in delaying most
of the modules it loads.  Some of the inbox-specific and
v2-specific stuff can be lazy-loaded, however, since this
will support mirroring non-inbox repositories, too.