Avoid encoding data into the campaignId by using a new property trackingInfo that can be encoded as JSON string and is open to future changes.

Data structures that are not relevant to the SDK should be transported as JSON string instead of JSON object. This affects the deviceEventState, trackingInfo and the reporting property.

Allow returning multiple campaigns in the response since this is a requirement for Webchannel which will be integrated in the future.

Only allow the new ems- prefix for header names.

In the response of the events endpoint properties containing the campaigns were renamed for consistency.

The reportingId was changed to be a JSON string property called reporting to be consistent with the push notification payload.