more usersnap issues

[ascott]

• update teaching text (was duplicated)
• remove newsletter signup box in side nav, just use button
• in create user flow, don't use user email as user name if one is not provided
• on user pages, and article pages, truncate user names if it is an email address (so we don't display publicly)
• replace copyright symbol with creative commons icon and link to license
• add link “News” to medium in hamburger and footer

fixes:

• Usersnap Feedback - Duplicated text in first section. usersnaps#338
• Usersnap Feedback - Just use button for newsletter on hamburger (not box with text). usersnaps#337
• Usersnap Feedback - Username should not display users email address. usersnaps#335
• Usersnap Feedback - @jesi should we be using the creative commons icon here, or the copyright icon? usersnaps#339
• add link “News” to medium in hamburger and footer #470

@jesicarson @dethe