add headless browser, closes #3

[JASONews]

add headless browser and unit test

[rpanah]

@JASONews I had a look at your branch just now. It seems like the code is just copied over from some repository other than a fork of Centinel and has not been formatted to comply with Centinel. Here are my comments:

• The code has zero comments. This is almost sure to make the code useless in the future.
  • add comments to the code
  • add Wiki pages to explain how to use/develop this primitive; it is not exactly trivial.
• The code and the directory structure presented here does not conform to that of Centinel at all.
  • rename and move the actual "primitive" to the root of primitives folder (hb.py -> centinel/primitives/headless_browser.py)
  • rename and move the unit test and unit test input files to the appropriate folders (hb.sh, input_list.txt, and test_hb.py -> centinel/unit_test/test_headless_browsing.py.txt.sh)
  • The driver code written to rest the code should be turned into a proper Centinel "experiment" (with standard Centinel-format input and output format) and put in the appropriate experiments directory.
• The "FOCTor" library included here is entirely copied from another repo. Can you just reference it in Git as a submodule instead? (look here)

[JASONews]

Sorry for the inconvenience, I'll add more comments and reorder the structure.