Update module documentation for 2.x and release 2.0-alpha1

Problem/Motivation

So many things are changing in 2.x, the documentation will definitely need a refresh.

Proposed resolution

Once we are happy with the state of the must-haves in #2949844: [META] 2.x Development roadmap, we should

- Update the project page with information about 2.x
- Create a documentation page with configuration instructions, views setup, developer information (with main API changes from 1.x), etc
- Update README.md file inside the module

and then finally create an alpha1 release.

Remaining tasks

User interface changes

API changes

Data model changes

Problem/Motivation

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes