Introduce new wasmer-configs crate

[theduke]

Implement a new crate wasmer-configs, which will hold:

• The package definitions previously located in wasmer-toml
  (currently located in https://github.com/wasmerio/wasmer-toml)
• the app.yaml Edge app configuration
• edge_util::headers::HEADER_APP_VERSION_ID (currently used by the CLI
• Edge updating

Currently we have problematic interdependencies between different repos, which cause significant friction and complications when working on new features.

This will simplify development and maintenance.