Implement stored user preferences.

[campb303]

After #15 is completed, there should be a mechanism for storing and syncing user based preferences across devices for settings such as dark mode and saved searches.

[campb303]

Several discussions have come to the need for syncing user preferences in a central location. The settings include:

• Dark mode setting
• Saved searches
• ItemTable column visibility
• ItemTable column reordering

[campb303]

Without a proper database, this can be implemented client side for a per device config.

[campb303]

Implementing a client side setting store would eventually need to be reworked to use a server side database solution and change how the application works. Instead, we can use SQLite server side and make queries via a database management tool that abstracts specific database engine workings like SQLAlchemy. Later we can simply switch the database backend while keeping the logic for the API and frontend the same.

[campb303]

API portion of this moved to ECN/webqueue2-api#9

Frontend item can be remade when API item is completed.