added OpenTrails Course sign-up form to last view of convert flow
updates to copy across converter flow, adding context, opening errors in new tabs, etc.
added a proper message if transformation does not succeed
updated copy and references for all converter and validator error messages
included helper copy regarding data uploads over poor connections
content authored for validator upload page
amended copy on 'bad-data' message pages to include missing optional properties
reverted validator headline copy to pass tests
updated readme.md
Merge pull request #71 from codeforamerica/content-v3

Content v3