Add/select by negative ID

[TheLastOfEugenes]

The idea is to add the possibility to select the last added credentials without knowing its idea, very useful if you don't want to use the tui or want to use it in functions/aliases.

Example: you just added new credentials with

exh add creds -u "user" -p "wrongpazz"
you can set those easily
exh set creds -i -1
you can modify quickly in case of error
exh edit creds -i -1

I seperated it from the last pull request in order to make modifications easier, please do tell me if it would have been better to do all these in one go.

[TheLastOfEugenes]

Je suis désolé je viens de voir que le premier commit était resté, heureusement cela ne concerne que 6-7 lignes.