evolution: add possibility to chose another file for the key or provide own key
The request is to:
- allow to pass another variable to use another file for the key
- allow to pass the key directly Proposal is to have 3 arguments for the methods:
- the string to be encrypted/decrypted
- a string specifying the variable in the file indicating the file to use (optional)
- a string giving the key (optional) If the second and third arguments are null, the default one is used. If the second argument is not null, the file for the variable is used. If the second argument is null but the third argument is not null, it is used as the key