[meta] Restructure integrations to their own directories

[rytilahti]

Move each integration to their own directory, containing the integration-specific implementation, data and test files.

This allows separate integrations to have their own data files stored without poluting the main package (see, e.g., #1094 for yeelight spec files), and make the integrations partially self-contained.
This also allows adding integration-specific, discoverable manifest files whose pros are discussed in another issue to be linked here.

Each integration should be stored under miio/integrations/<name> which can contain several source files including unit tests and any other data.

Status

• Yeelight (create separate directory for yeelight #1160)