graphviz dependency

[aaronmarkham]

Description

We have various documents that have graphviz as a dependency for MXNet, both as a system package and a python package, and without a version number specified.

I recently ran into an issue on the nano while working on the instructions where trying to bind Python to the libmxnet.so binary, it failed because my graphviz version exceeded the allowed range of graphviz<0.9.0,>=0.8.1. I had 0.10.1. This is what any new user is going to get when following most source installation instructions. Which means they'll fail.

1. Why do we have this range?
2. If we were going to pin a version, what would it be? 0.8.4 is last release in current required range.
3. Why do we require both system and python packages?
4. Do we even need this dependency with MXBoard being a superior alternative?

[mxnet-label-bot]

Hey, this is the MXNet Label Bot.
Thank you for submitting the issue! I will try and suggest some labels so that the appropriate MXNet community members can help resolve it.
Here are my recommended labels: Feature

[marcoabreu]

Test