Small cleaning of codes

[Arthur-Milchior]

First, I wanted to replace isEmpty by containsNoCard. It seems interesting to note that this may still contains non-default note-type and decks, and still consider the collection empty.

This makes me look at Pairs, and found that, often, destructing the Pair seems more readable to me than using .first and .second. Especially when it eiher allows to have a single non-null assertion, or allows to have name value instead.