Extend list capacity, initialization and limitations

[phorward]

0a2879f was a simple change that allows to extend a list automatically to arbitrary content by assigning to an index.

This behavior could be made more customizable:

• change the default value that is used for newly added cells (instead of using Value::Null)
• set an (optional) limit until which further cells are automatically added or a runtime error occurs
• initialize a list with a given number of values

This issue is used to bundle commits related to this.