Multi-key import feature (#1201)

* use PathBuff instead of &str

* collect to path instead of mutating it

* switch to &Path instead of &PathBuf

* implemented multi-key imports support

* remove unnecessary line

* update rpassword

* fix imports

* trim input and print imported key

* return error with code 1 for KeyExists

* return both correct code and the message

* remove into()

Author: leviathanbeak