Clean `cozy-keys-lib` usage in other apps

[Ldoppea]

Some methods from cozy-keys-lib are not used anywhere while other apps implement similar methods:

• WebVaultClient.changePassword() is not used by other apps.
  • cozy-settings implements a similar method that may be replaced by cozy-keys-lib version.
  • cozy-pass-web implements a forceSetVaultPassphrase() method that is prety similar but doesn't handle currentMasterPassword and should be implemented in cozy-keys-lib as a setPassword() method.
• cozy-pass-web has code to handle unconfirmed organization with no key that should be moved on cozy-keys-lib so cozy-keys-browser can also use it. More info : Feat/hide no key orgs cozy-pass-web#37 (review)