Create a system for storing connection-specific preferences

[thoughts3rased]

Currently, outside of the hostname and credentials there's no way that we can currently store per-connection preferences.

As the application progresses through development, we may discover valid use cases where the app should behave differently for different connections and that we want to provide the user with the opportunity to configure this behaviour for their connections.

As mentioned on #481, a user should be able to configure whether or not a connection should be allowed to be established if it is insecure. This will be an excellent first option to give to users.

The requirements of this feature are as follows:

• There should be a "connection properties" screen to allow the user to configure settings for a connection
• Settings should be easily added code-side
• Different setting values should be available (checkbox, int, string, etc.) (maybe an Enum type?)
• These settings should be accessible before and after connection to allow tweaking of options that may break connections (future-proofing)

[thoughts3rased]

Also related to #534

[boswelja]

Seems reasonable, I just want to add

• This should be a new module under feature
• This should exclude Create a system for managing allowed cleartext connections #534 - we can expose a setting to control it in the same screen, but I don't think it makes sense for the cleartext controls to live in connection-specific settings (it would make it harder to check whether a given connection is allowed)