Start restructuring audio playback, add some tests for audio

Fixes #15 where audio was not stopped on logout

test/cljs/airsonic_ui/test_helpers.cljs

@@ -6,3 +6,14 @@
   [cofx ev]
   (let [all-events (conj (get cofx :dispatch-n []) (:dispatch cofx))]
     (boolean (some #(= ev (if (vector? ev) % (first %))) all-events))))
+
+(defn rand-str
+  "Generates a random string; ported from https://stackoverflow.com/a/27747377/2345852"
+  ([] (rand-str 40))
+  ([len]
+   (let [arr (js/Uint8Array. (/ len 2))]
+     (.. js/window -crypto (getRandomValues arr))
+     (.. js/Array
+         (from arr #(-> (str 0 (.toString % 16))
+                        (.substr -2)))
+         (join "")))))