Correct Grafana dashboard - disk I/O

exports: riemann export implemented and documented

This patch introduces a new export method for sending metrics to
__Riemann__ server using _TCP_ protocol. The module can be enabled like
all the other exports in __Glances__, specifying the `--export-riemann`
option.

Sending metrics to Riemann requires
[bernhard](https://github.com/banjiewen/bernhard) that is
the most popular _Riemann client_ written in python.

In the configuration file you can only specify the `host` and `port`
that riemann is listening for new connections on. Later new options are
planned to be added like __SSL__ support and __UDP__.

Documentation and manpages are refreshed according to the modifications
in the config options and introducing the usage of Riemann export.
Signed-off-by: NGergő Nagy <grigori.grant@gmail.com>

Update all affected imports accordingly.

The psutil_version instance variable was erroneously declared as private
(using name mangling).

Add conda package maintainer (conda-forge)

authors: Update Debian link for Glances package (use tracker.d.o)

Thanks @nicolargo for the mention/addition :)