Vertical tabs widget uses same entity property of a list for the label of a tab and the "add entity" button text

[e-me]

Hello, we've came across a translation issue with languages that have cases (i.e. Greek).

Description:
The vertical tabs widget uses the entity property of a list for both - the label of a tab (https://github.com/h5p/h5p-editor-vertical-tabs/blob/master/vertical-tabs.js#L283) and for the "add entity" button text (https://github.com/h5p/h5p-editor-vertical-tabs/blob/master/vertical-tabs.js#L32) and that this may cause issues with Grammar in different languages as one of them has to be nominative and the latter one genitive.

Possible solution
A separate field for a list might be useful, could also be a separate field for the vertical tabs widget parameters if it won't get purged by the h5p cli tool, etc.

[e-me]

Any inputs on this issue?