Update french.json

Looked for possible mistranslations based on the word "wallet".
Fixed mistranslations, sometimes caused because of the difference between "a wallet" and "My Wallet".
Sometimes just fixed the surroundings of what was found.
Left "Brain Wallet" as is, as "Portefeuille Cerveau" would feel weird in french. A translation may need to use another word than "brain" as basis.
On the other hand, translating "Paper Wallet" as "Portefeuille Papier" feel ok.

I will have to continue that from strings / wallet_app / modals / watch_only_warning_p3