Add database configuration

[bdashore3]

A database is far more performant than using many JSON files since file reads won't have to be done all the time.

Key encryption will be accomplished later and a method will be made to encrypt all current keys in the database.

References #6

[bdashore3]

UserJson creation is broken, further commits required for systemd and userjson fixes.

[bdashore3]

Tested with single-user and database configurations.

• Manual manga JSON generates properly
• User JSON is removed after database insert
• Everything inserts properly inside the database
• Single user fallback occurs if no credentials/db url is provided

Resolves #6