Import: Single and multiple author import flow

Testing https://github.com/Automattic/wp-calypso/pull/3133 and capturing import flow.

Importing a single author site to a single author site. Macnchrome using https://codex.wordpress.org/Theme_Unit_Test import data. Clean run.

 Importing a multi-author site to a single author site. Macnchrome using http://wptest.io/ data. Import fails silently. Console shows “Unhandled promise rejection Error: Author mapping missing or incomplete.”

Todo: captions

#import, #importer, #needs-captions

#3077-gh-wp-calypso