Merge branch '47-use-dark-theme' into 'master'

Resolve "Use dark theme"

Closes #47

See merge request !43

assets/styles/app.scss

-@import "~bootswatch/dist/pulse/variables";
+@import "~bootswatch/dist/darkly/variables";
 @import "~bootstrap/scss/bootstrap";
-@import "~bootswatch/dist/pulse/bootswatch";
+@import "~bootswatch/dist/darkly/bootswatch";
 
 table.table-fixed {
     table-layout: fixed;
@@ -18,7 +18,7 @@ table.table-fixed {
 }
 
 .spotify-image > img {
-    border: solid 1px #888;
+    border: solid 1px #444;
     text-align: center;
     max-height: 1rem;
     max-width: 1rem;