Improve error handling

[maxekman]

Description

Improve errors by:

• Providing more details such as aggregate ID, version, related events etc.
• Printing of more detailed error information.
• Providing operations for errors to DRY up error descriptions.
• Use fmt.Errorf() to wrap errors instead of BaseErr.
• Return errors as pointers.
• Use errors.As/Is where possible.
• Remove unneeded error vars.

Affected Components

• All errors.

Related Issues

Fixes #284
Fixes #286

Solution and Design

Steps to test and verify

[coveralls]

Coverage decreased (-1.0%) to 68.321% when pulling 139df9a on maxekman:ISSUE-284/remove-base-err into d45655a on looplab:main.