[FAU-422] Support core "Quote" block

[tyrann0us]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes/features)
• [ ] Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Feature

What is the current behavior? (You can also link to an open issue here) https://inpsyde.atlassian.net/browse/FAU-422 The "Quote" block is not supported in content fields.

What is the new behavior (if this is a feature change)? The "Quote" block is supported and persisted in content fields.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) No.

Other information:

• Related, dependent PR: https://github.com/RRZE-Webteam/FAU-Studium-Common/pull/4
• As part of the Boy Scout rule, this PR also includes a fix for a regression introduced in #126 (internal discussion)