CellParser: Support list nesting and quote escaping

[geoo89]

Currently, two list separators are supported, allowing for a nesting depth of 2 (when encoding lists in cells).
Consider adding brackets [ ] to support deeper nesting (note: brackets are for grouping, and do not define lists themselves).
Examples:
▪ 1 → 1
▪ [1] → 1
▪ 1;2 → [1,2]
▪ [1;2] → [1,2]
▪ [1;2]; → [[1,2]]
▪ [1];[2] → [1,2]
▪ [1;];[2;] → [[1],[2]]
▪ [2|3];[3|4] → [[2,3], [3,4]]
Also consider supporting quotation marks as an alternative to escaping special characters with backslashes.