Add login(), logout(), and whomai() functions
Allow optional email on login. Use that or last email as default in email prompt.
Merge branch 'dev' into feature/cli-login-logout-commands

Conflicts:
	solvebio/test/test_login.py
Address flake8 warnings on test/test_login.py
remove unused methods in test_login
Merge pull request #45 from solvebio/feature/cli-login-logout-commands

Login/Logout via IPython