Empty ad block is not hidden

Problem/Motivation

Even if there's no ad available for an ad block, the block is still rendered in the content and may lead to spacing

Steps to reproduce

Have no ads, just place the blocks for a certain size

Expected:
Do not show the block

Actual:
The blocks are shown

Proposed resolution

Hide / remove blocks if empty

Of if this needs to be configurable, add an option in the block settings: "Hide block if there are no matching ads"

Remaining tasks

User interface changes

API changes

Data model changes