Refactor last_fm configuration

Move all configuration outside of the LastFm module, so that it's not
polluted with references to the parent music_library application.

lib/last_fm/refresh.ex

@@ -5,14 +5,14 @@ defmodule LastFm.Refresh do
 
   alias LastFm.Feed
 
-  @refresh_interval System.convert_time_unit(60, :second, :millisecond)
-
   def start_link(config) do
     GenServer.start_link(__MODULE__, config, name: __MODULE__)
   end
 
   @impl true
   def init(config) do
+    config = Map.new(config)
+
     if enabled?(config) do
       {:ok, config, {:continue, :refresh}}
     else
@@ -25,12 +25,12 @@ defmodule LastFm.Refresh do
     case config.api.get_recent_tracks(config.user, config.api_key) do
       {:ok, tracks} ->
         Feed.update(tracks)
-        Process.send_after(self(), :refresh, @refresh_interval)
+        Process.send_after(self(), :refresh, config.refresh_interval)
         {:noreply, config}
 
       {:error, _reason} ->
         # TODO: think about failure scenario - error is logged at the API level
-        Process.send_after(self(), :refresh, @refresh_interval)
+        Process.send_after(self(), :refresh, config.refresh_interval)
         {:noreply, config}
     end
   end
@@ -40,12 +40,12 @@ defmodule LastFm.Refresh do
     case config.api.get_recent_tracks(config.user, config.api_key) do
       {:ok, tracks} ->
         Feed.update(tracks)
-        Process.send_after(self(), :refresh, @refresh_interval)
+        Process.send_after(self(), :refresh, config.refresh_interval)
         {:noreply, config}
 
       {:error, _reason} ->
         # TODO: think about failure scenario - error is logged at the API level
-        Process.send_after(self(), :refresh, @refresh_interval)
+        Process.send_after(self(), :refresh, config.refresh_interval)
         {:noreply, config}
     end
   end