Handle clears_artifact_provides in mender client

Acceptance criteria:

• Implement handling of clears_artifact_provides in the artifact format.
• All the artifact_provides stored in the DB are matched against all entries in the attribute, glob-style.
  • When committing artifact, existing provides that had no matches must be retained
  • When committing artifact, existing provides that matched must be erased
  • Provides that come with the current artifact (even if in a different payload) must always be retained, even if they match
• If an artifact comes with no clears_artifact_provides (nil value), then the client must behave as if '*' was specified, in other words match everything. This is to preserve backwards compatibility.

Feature branch name: feature-partial_updates