Thanks Microsoft Windows to not support some filenames

Let CSI keep latest stanzas of each given full JID

Fix routing of groupchat and headline messages

This is the case if running ejabberd from development directory
when code:lib_dir(ejabberd) returns {error, nad_name}.

Fix order of starting supervisors.

Keep the latest stanzas of each given full JID, rather than dropping
them when stanzas from a different resource are received.  This change
makes sure the recipient receives the latest status of all clients of
each contact.  It also ensures the recipient will see the current list
of occupants of joined MUC rooms.

Use maps:size/1 rather than keeping track of the size ourselves.

Fixes #1624

ExtMod should be loaded before GenModSupervisor because ext_mod adds proper paths to ebin from modules (ejabberd-contrib).
Without this change you have to add -pa parameter with path to module's ebin.

As per RFC 6121, silently drop headline messages sent to the bare JID of
an offline user or to the full JID of an unavailable resource.

As per RFC 6121, don't (re)route groupchat messages sent to a bare JID
or to an unavailable resource.

Fixes #1652

Now that plugins directly use ejabberd_mnesia and can include their own
transform handler, we don't need pubsub_migrate anymore.

People upgrading from 2.1.1x version must upgrade to 17.01 first.
pubsub_migrate module remains to support any manual process requiring it