Add MC xmax info

[kbruegge]

Adds the xmax info to the MC container. This can be used as soon as the new pyhessio is used in ctapipe with this PR cta-observatory/pyhessio#62

[kosack]

I'll build a package for the new pyhessio and upload it shortly, then this should work.

[kosack]

there is now a pyhessio-2.1.0 package in the cta-observatory channel (for linux, mac, and py35, py36). Try updating the environment.yml and setup.py to require >=2.1 and see if it works. I haven't done any testing.

[codecov]

Codecov Report

Merging #759 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #759      +/-   ##
==========================================
+ Coverage   69.49%   69.49%   +<.01%     
==========================================
  Files         198      198              
  Lines       10708    10710       +2     
==========================================
+ Hits         7441     7443       +2     
  Misses       3267     3267

Impacted Files	Coverage Δ
ctapipe/io/containers.py	100% <100%> (ø)	⬆️
ctapipe/io/hessioeventsource.py	95.16% <100%> (+0.03%)	⬆️

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[kbruegge]

It works 👍

[kosack]

Great! Looks like it works. I'll merge it in.