collectd: enable a bunch of plugins (by adding more deps)

These are plugins that are internal to collectd; they are bundled in the
source archive. Without this, many of the collectd plugins advertised on
their homepage don't actually work, so I think we should add this.

This change increases the closure size from 129 MiB to 621 MiB. The size
of the collectd store path itself goes from 2 MiB to 2.9 MiB.

Users wanting a smaller closure size can set some (or all) of the
optional inputs to "null" using ".override".

List of new plugins:

  amqp
  apache
  ascent
  bind
  curl
  curl_json
  curl_xml
  dbi
  dns
  iptables
  libvirt
  lvm
  memcachec
  modbus
  mysql
  nginx
  notify_desktop
  pinba
  ping
  postgresql
  redis
  rrdcached
  rrdtool
  sensors
  sigrok
  varnish
  write_http
  write_redis
  write_riemann
collectd: update meta attributes

Don't repeat package name in description, add maintainer, ...