Add dockerfile

[janjagusch]

Closes #46
Closes #44

Docker image can be built with:

docker build -t gdv.xport -f Dockerfile .

Docker container can be run with:

docker run -p 2517:2517 gdv.xport

If this PR gets accepted, documentation should get updated as well.

[codecov-commenter]

Codecov Report

Merging #47 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #47   +/-   ##
=========================================
  Coverage     90.75%   90.75%           
  Complexity     1309     1309           
=========================================
  Files           168      168           
  Lines          7402     7402           
  Branches        363      363           
=========================================
  Hits           6718     6718           
  Misses          534      534           
  Partials        150      150           

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[coveralls]

Coverage remained the same at 92.786% when pulling 079d9f3 on janjagusch:add-dockerfile into 6c92624 on oboehm:master.