Merge Portals-JS branch

[jspenger]

• Portals is now cross-building for both JS/JVM
• There is now a API for Portals: PortalsJS
• What is missing, but will be done soon, is CI support for the PortalsJS API
• This closes a bunch of issues relating to PortalJS

[jspenger]

Replacing this with a new PR with a squashed git history #194