Fine-tune password generation options

[dlajarretie]

The lib allows to set the following parameters when generating a password:

General rules

• length (default : 20 characters)
• human-readable (default: false)
• avoid similar characters (default: false)

Content rules

• containing numbers (default: true)
• containing symbols (default: true)
• containing mixed case (default: true)
• strict mode = containing at least one of each the enabled content rules (default: false)

We should add the UI to be able to change these settings when generating a password.
The user should be able to customize the defaults in settings.
The configuration for each secret should be stored.

[dlajarretie]

We could maybe cover #62 as part of this

[dlajarretie]

Implemented in #151