Harmonize forest task add and forest note add

[baptistemehat]

As of now these two commands, which have similar APIs, have different argumernts that can lead to confusion:

forest task add <task-name>   # adds a task to current tree
forest note add <tree-name>   # adds a task to the specified tree, or the current one if not specified

I think these commands should share the same behaviour, ie. forest task add should take the tree name as the first positional argument, or forest note add takes a title as its first positional argument