allow renaming of tasks

[behinger]

instead of only selecting tasks, I think it would be helpful to also be able to rename them

e.g. allow for this:
tasks = { "Default":"freeviewing", "freeviewing":"freeviewing"}

• implement this renaming (optional! if a normal list is found, it should just select"
• in case multiple values are identical (length(unique(values)) != length(values)) be sure to check that not the same task exists within one dataset -> this would lead to overwriting of data!
• document this in the docs & the default toml file