extract user settings

[adrian-schnell]

move all settings depending a user to a separate table

• language
• theme

[adrian-schnell]

changes on the current code:

• rename PUT /user to PUT /user/settings
• wrap user settings in "settings" - e.g.:

{
    "userId": "3a29a279-f596-434d-8634-a2fccbd2e651",
    "settings": {
        "language": "de",
        "theme": "light"
    },
    "vaults": [... ]
}