[enhancement] allow for managing API keys for all services at once

[Inderix]

Breadboard currently allows for easily switching between sources directly before performing a search, but in the settings you still need to change your default source before editing each API key and its not immediately obvious that you can have an API key for each service. Maybe a tabbed interface somewhere to switch between source-specific settings?

This would largely not solve any serious problem, but would resolve the jank of changing your default source, setting an API key, and repeating until each source the user wants a key for, has one, and make it clearer to the user that you can set API keys for all sources currently available.

[apex2504]

I agree the current flow isn't great. The settings page is starting to get a little unwieldy so I think at some point I'll look into splitting it off into dedicated pages, at which point I can implement this too.