Fix handling of angle brackets in mod_muc_log when outputting plaintext

Previously, nicks surrounded by angle brackets (see Nick2 on line 323)
were being lost when outputting plaintext, because htmlize() was ignoring
them then fw() was stripping them as HTML tags.
Support middleware and module option configuration in ejabberd_cowboy
Example config for running a static file web server

This should provide equivalent functionality to mod_http_fileserver in
P1 ejabberd.
Added a first version of Cassandra MAM backend.
Added query_refs_count for mod_mam_muc_ca_arch.
Added new book filter_local_packet. Fixed {badarg,[{ets,member,['ejabberd_users_muc.localhost',{<<alicesroom>>,<<muc.localhost>>}],[]} during sending a MUC message.
Added a special version of mod_mam_cache_user for MUC.

Added an empty stop_server function.
Added mod_mam_odbc_server_user: archive id assignor for multiple hosts.
Added unique constraint for mam_user and mam_server_user tables.
Deleted MAM_ARCHIVE_PRESENCE. Splited is_complete_message into several ones.
Added seestar into release dependencies.
Fixed wrong function name.
Added prepare_user_id/1 for mod_mam_ca_arch.
Added mod_mam_muc_ca_arch:select_worker/2.
Merge branch 'arc-mam-mods' into arc-mam-ca
Added mod_mam_muc_ca_arch:prepare_room_id/1.
Added servers config variable for mod_mam_muc_ca_arch.
Select worker based on archive id in mod_mam_muc_ca_arch.
Deleted prepare_room_id.
Added mod_mam_con_ca_arch.