Saves password to keyring

Closes #96 and deprecates password field in config
Disambiguates jrnl.update_config and install.update_config
Remove tests for having password in config
Only updates config locally on encrypting and decrypting
Tests for storing password in keychain
User plain text keyring for testing
Updates readme
Only soft-deprecate passwords in config
Tests for soft-deprecating passwords in config
Merge pull request #99 from maebert/96-keychain

Saves passwords to keyring