Placing APIs under /api instead of top level

This is a WIP commit - it breaks the JavaScript libs for streaming and vtkweb.
Adding abstract way to generate API urls
Updating stream.js to make use of tangelo.apiUrl()
Updating vtkweb.js to use tangelo.apiUrl()
Updated docs to reflect API sequestration
Merge branch 'sequester-apis' into develop

Closes #370