Rename fcmdr_service_read_config()

...to fcmdr_service_init_profile_sources().

That profile sources come from a config file is an implementation
detail.  This is more descriptive for the initialization sequence
in the construct() method.
FCmdrService: Rename some path definitions.
Add fcmdr_profile_new_from_node().

Creates an FCmdrProfile from a JsonNode of type JSON_NODE_OBJECT.

This is to assist profile cache loading, since we cache all the profiles
in a JSON array.
Add fcmdr_service_init_profiles().

Reads cached profiles from the previous session.  This is called on
startup before fetching remote profiles in case remote profiles are
unavailable, and also to avoid applying unchanged profiles.