Unify module/subsystem process names

[erszcz]

Currently, when listing processes under ejabberd_sup we see that some of them are called ejabberd_mod_* while some mod_*:

> rp(supervisor:which_children(ejabberd_sup)).
[{'ejabberd_mod_muc_sup_fake.domain.one',<0.631.0>,supervisor,[ejabberd_tmp_sup]},
 {'mod_ping_fake.domain.one',<0.618.0>,worker,[mod_ping]},
 ...]

It spans from the fact that some modules use a PROCNAME macro in calls to gen_mod:get_module_proc/2 while others use just the MODULE macro.

While not a high-priority issue, it would be nice to unify the process names, so that they always start with the ejabberd_* prefix, e.g. by introducing the PROCNAME macro to modules which don't use it.

[arcusfelis]

We are working on it, sorry for a delay.