refactor(core.cloud): Cloud bundles refactor

[pierantoniomerlino]

This PR is a refactor of the core and core.cloud bundles.

Related Issue: This PR fixes/closes N/A

Description of the solution adopted: In order to simplify the core and core.cloud bundles, this PR does the following actions:

• the command.cloudapp package and service is extracted to a new core.cloud.command bundle
• the core.cloud bundle is renamed to cloudconnection.kapua.mqtt.provider
• the DataService and related packages are moved to the new cloud.base.provider bundle
• the 'MqttTopicUtilclass is moved from thecore.utilpackage to a newcore.data.util` one.

The tests and references are accordingly updated.