#22 multiple master passwords

[Brett Wuth]

Allow multiple master passwords. Assumes that the feature which encrypts only the embedded passwords is implemented (see separate feature request). Allow multiple records for the same password, encrypted against different master passwords. Each record would need a field to identify which master password was used.

Use case:

An organization wants to keep a single JPasswords database for multiple users. Some embedded passwords are only accessible to some users. (Each user would have their own master password.)