Make the key generation parameters optional

[le-git-imate]

Description of issue or feature request
The key generation function does not get all parameters from the user. Instead it uses predefined values as follows:

   key expiration: 0
   key size: 2048
   passphrase: ""

Current behavior

• The key generation process allows the user to neither set a key expiration nor to pick the key size nor to set a key passphrase.

Expected behavior

• Update the setup UI to get new key parameters.
• Use the parameters during the key generation process
• Update the key retrieval process