spotify: Add config schema
local: Add default config and config schema
stream: Add default config and config schema
mpd: Add default config and config schema
lastfm: Add default config and config schema
mpris: Add default config and config schema
http: Add default config and config schema
docs: Tweak module docs formatting
docs: Update extensiondev docs to match real usage
local: Return schema
Merge pull request #381 from jodal/feature/add-ext-config

Add default config and config schemas to extensions