Problem/Motivation
For themers it is really important to distinguish the different block types.
Proposed resolution
Add a css class to blocks, which indicates which type is used.
For example: If you have a block type "Banner" then a css class "block--type-banner". I don't know the drupal css guidelines, so the classname is just a proposal.
Remaining tasks
[ ] Implement this
User interface changes
None
API changes
None
Data model changes
None
Should be a small fix with no breaking changes.