Installer tweaks and a pypo bugfix

* Moved all the remaining DEB requirements into the requirements files
* The installer should now be distro agnostic (unless you ask it to
  install third-party deps for you)
* Fixed pypo not being able to find replaygainupdater
* Tweaked a bunch of styling for the installer

airtime_mvc/public/css/setup/config-check.css

@@ -3,13 +3,11 @@
 }
 
 .table {
-    padding: 0;
+    padding: 5px;
     margin: 1em 0 0 0;
 }
 
 .checklist {
-    overflow: auto;
-    height: 50%;
     min-height: 200px;
 }
 
@@ -22,8 +20,12 @@
     width: 20%;
 }
 
-.description, .solution {
-    width: 40%;
+.error {
+    color: red;
+}
+
+.description {
+    width: 300px;
 }
 
 .check {