Feature/add new activities

[ahouseholder]

Hi there,

(resubmitting #6 after fixing lint warnings)

I just used the h1 module to retrieve a bunch of reports out of HackerOne. It worked quite well, but I hit into three separate exceptions on different records.

activity-cve-id-added activity-nobody-assigned-to-bug duplicate_report_id should be optional The two activities are present in the data although they are undocumented in the H1 API docs. I also ran across at least one report object that contained an activity-external-user-joined object without the duplicate_report_id attribute, so it seems like marking it as optional is the obvious fix.

[ahouseholder]

Test data blobs added for the two new activities in commit b2c2dc0

[ahouseholder]

Finally got it right. :-)