Add headless Dockerfile

[polyedre]

The current docker image at https://hub.docker.com/r/cyberwatch/wapiti cannot use the new --headless flag because firefox and firefox-geckodriver are required.

I tried to update the current Dockerfile to install both firefox and firefox-geckodriver, but the size of the image went from 190MB to 650MB. Instead, this PR adds a Dockerfile dedicated to build a wapiti image that supports headless mode.

This has been tested by running the following command with the build image:

docker run wapiti -u http://angular.testsparker.com/ -m "sql" -v 2 --store-session=sessions/ --store-config=sessions/ --flush-session --color --headless hidden

Closes #320

[codecov-commenter]

Codecov Report

Merging #321 (81a6d2a) into master (891f5e7) will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #321      +/-   ##
==========================================
+ Coverage   74.83%   74.89%   +0.06%     
==========================================
  Files          94       92       -2     
  Lines        9269     9252      -17     
==========================================
- Hits         6936     6929       -7     
+ Misses       2333     2323      -10     

Impacted Files	Coverage Δ
wapitiCore/__init__.py
wapitiCore/net/__init__.py
wapitiCore/main/wapiti.py	58.85% <0.00%> (+0.28%)	⬆️

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