Improve Dockerfile

[sammcj]

• Replace deprecated MAINTAINER command with LABEL
• Reduce apt-get installs to a single layer and do some cleanup
• Reduce pip installs to a single layer
• Reduce git clone to a depth of 1 (to reduce size over time)
• Slightly helps with https://github.com/Hellowlol/bw_plex/issues/25

It's still based on Ubuntu, which is not something I recommend for Dockerfiles (or a distribution for that matter but that's another discussion) - however most of the weight is coming from the libLLVM requirement (which I'm guessing is still required after install?), so if that's required, it's still going to be large:

--- /usr/lib 
-----------------------------------------------
                         /..
  333.8 MiB [##########] /x86_64-linux-gnu
   94.2 MiB [##        ] /python3.6
   84.8 MiB [##        ] /gcc
   21.7 MiB [          ] /git-core
   13.5 MiB [          ] /python3

--- /usr/lib/x86_64-linux-gnu
-----------------------------------------------
                         /..
   58.3 MiB [##########]  libLLVM-6.0.so.1
   32.7 MiB [#####     ] /dri
   25.7 MiB [####      ]  libicudata.so.60.2
   19.6 MiB [###       ] /perl
   13.1 MiB [##        ]  libavcodec.so.57.107.100
   10.4 MiB [#         ]  libx265.so.146

Note that python's libpython3.6m is also relatively large, I'm not a python dev so I'm unsure of it's requirements, if it's not required after install, perhaps it could be purged after the pip install phase, but I'm guess it is required:

--- /usr/lib/python3.6/config-3.6m-x86_64-linux-gnu
-----------------------------------------------
                         /..
   36.2 MiB [##########]  libpython3.6m.a
   35.5 MiB [######### ]  libpython3.6m-pic.a
   84.0 KiB [          ]  python.o

Note: this still has one linter warning 'Consider using a --no-install-recommends when apt-get installing packages' but that does seem to break the build and I didn't spend further time to figure out which recommended package is actually required.

[codecov[bot]]

Codecov Report

Merging #57 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #57   +/-   ##
=======================================
  Coverage   77.16%   77.16%           
=======================================
  Files           8        8           
  Lines        1187     1187           
=======================================
  Hits          916      916           
  Misses        271      271

---

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[Hellowlol]

Thanks alot. Im really out of my depth regarding dockers :)

[sammcj]

No problems, obviously because packages aren’t pinned to versions YMMV over time but that’s already the case.