Tag callback, use error message, add context

Based on v1.7.0 of notamedia/yii2-sentry, this release adds the following:

Added

• Add tagCallback config option to add or change tags on a global level.

Fixed

• Fixed log events with "" so the message can be derived from either the "error" key or, as a last resort, the whole message serialized as json.
• Use Sentry "context" rather than "extras" due to the latter no longer being functional.