Update schemas from openfec swagger documentation

[esonderegger]

This PR updates the __init__ method for each of the classes in pyopenfec to have the fields that are shown in the "response class" for each data type at https://api.open.fec.gov/developers/.

The reason I got started exploring with this was that our reporters prefer the html_url links to the pdf_url links for reports and filings.

Instead of just adding those fields, I figured I would see what else was different between the models and the what is currently in the swagger documentation.

To test the new fields are indeed present, run:

from pyopenfec import Committee
committees = Committee.fetch(designation='P', candidate_id='H4VA10089')
for committee in committees:
    reports = committee.select_reports(report_type='Q1', year=2018, is_amended=False)
    for report in reports:
        print(report.html_url)

and verify that the link takes you the 2018 Q1 report for Barbara Comstock.

I suppose there is a chance removing fields that are no longer returned by the API could break some code that expects those attributes to be present. I fear it would be confusing to leave them in, though.