Optionally store start/end dates when legislator obj is initialized. Then use them to create default role.
Merge branch 'master' of github.com:opencivicdata/pupa

Conflicts:
	pupa/scrape/helpers.py
Merge branch 'master' of github.com:opencivicdata/pupa
Merge branch 'master' of github.com:opencivicdata/pupa
Initialize org.classification to empty string rather than None
Add classification kwarg into Committee instantiation in tests