Add "connected since" and "member since" to user data

[oubiwann]

Note: user data, not livings/character data.

Use the same file that stores the password. This will require a bump in the version of the file format.

Tasks:

• Bump file format version
• Update user state
• Update user data model
• Update character state
• Update character data model
• Update login functions to generate these
• Add server functions to extract the data
• Add shell commands to query these

Depends on:

• Support multiple versions of file formats (file-based storage) #54

Part of:

• Harmonize and update existing storage API #34

[oubiwann]

Done.