[WIP] lesson/tutorial migration (group 1 tutorial migration)

[andy-esch]

@mehak-sachdeva @ztephm, use this branch for moving over content

Progress:

• [x] Creating and managing multilayer maps (mehak) #388
• [ ] Merging datasets (andy) #392 -- work in progress
• [x] Importing Shapefiles (added to multilayer maps lesson -mehak) #391

[csobier]

Staging output of PR: http://content-migration.academy.carto-staging.com/academy/ (I made some comments in the markdown file of the last commit)