Implement changes for MapMap 1.0

[aalex]

We are in a series in breaking changes while preparing for the release of MapMap 1.0 !

Changes

• Use the new naming system in OSC messages #474
• Use JSON for state saving #595
• Change "paint" to "source" and "mapping" to "layer" in OSC messages #451
• Change the organization's domain name for the settings file #600

Documentation to update

• Update the documentation for 1.0 #594
• Add Art Plus Code as a sponsor #597
• Indicate Alexandre Quessy as the new lead developer #596

Cleanup

• Remove prototypes from the main repository #593
• Merge CONTRIBUTING.md and HACKING #440

Other new features

• MCP connector #598

See also

The 1.0 milestone has some other minor tasks in it: https://github.com/mapmapteam/mapmap/milestone/8