Allow multiple property values via TypoScript

[brotkrueml]

Is your feature request related to a problem? Please describe.

Like with the API or the view helpers it should be possible to add multiple values with TypoScript, like:

"availableLanguage": ["en","de"]

Describe the solution you'd like

Preferable would be an array syntax known from TypoScript:

properties.availableLanguage {
    10 = en
    20 = de
}

The properties should be stdWrap'able.

Acceptance criteria

• [x] Via TypoScript multiple values for one property can be defined.
• [x] The documentation reflects this change.
• [x] A feature entry to the changelog is available.