add vitables to user environment

[kosack]

fixes #1340 , Just adds the vitables app (viewer for HDF5 files like those produced by ctapipe) to environment.yml

Rationale: we currently ask users & developers to set up their environment using environment.yml (rather than just conda install ctapipe), which includes packages that go beyond the required ctapipe dependencies, adding useful utilities like pandas and jupyter (also needed for documentation building). This env will likely also be published on anaconda.org (as ctapipe-0.8-env or similar), for easy user setup.

In the future, we might want to separate the testing environment from the recommended user environment, but for now they are the same.

[codecov]

Codecov Report

Merging #1344 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1344   +/-   ##
=======================================
  Coverage   91.10%   91.10%           
=======================================
  Files         183      183           
  Lines       12548    12548           
=======================================
  Hits        11432    11432           
  Misses       1116     1116           

Impacted Files	Coverage Δ
ctapipe/tools/stage1.py	85.59% <ø> (ø)
ctapipe/core/container.py	89.04% <100.00%> (ø)
ctapipe/io/hdf5tableio.py	95.00% <100.00%> (ø)
ctapipe/io/tests/test_hdf5.py	97.87% <100.00%> (ø)

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