Integrate centroid function from Bob Braswell into the package

[aiorazabala]

Code in #229 needs a lot of work for integration (this issue is a re-wrap of #15 ):

• Write help page
• Update NAMESPACE file
• Create example
• Test results against results in PQMethod, for lipset and another dataset validate centroid extraction vis-a-vis PQMethod #227
• Integrate additional rotation method in qmethod() function enable alternative extraction methods as an option to qmethod() #224
• Conduct testing with varying arguments and odd datasets check that existing plots, functions work with centroid-extracted data #226

Other (more complex) related issues are #225 (Cookbook) and #228 (Manual reflection).