Add the beginnings of charts

This commit adds a lot of files, but most of them have no impact on any
other code. The thrust here is to start creating chart pages showing
which tracks and artists were most played for various time periods. Lots
still not working, but we're getting there.

vrobbler/templates/music/artist_detail.html

@@ -0,0 +1,72 @@
+{% extends "base_detail.html" %}
+{% load mathfilters %}
+
+{% block title %}{{object.name}}{% endblock %}
+
+{% block details %}
+
+<div class="row">
+    {% for album in artist.album_set.all %}
+    {% if album.cover_image %}
+    <p style="width:150px; float:left;"><img src="{{album.cover_image.url}}" width=150 height=150 /></p>
+    {% endif %}
+    {% endfor %}
+</div>
+<div class="row">
+    <p>{{artist.scrobbles.count}} scrobbles</p>
+    <div class="col-md">
+        <h3>Top tracks</h3>
+        <div class="table-responsive">
+            <table class="table table-striped table-sm">
+            <thead>
+                <tr>
+                    <th scope="col">Rank</th>
+                    <th scope="col">Track</th>
+                    <th scope="col">Count</th>
+                    <th scope="col"></th>
+                </tr>
+            </thead>
+            <tbody>
+                {% for track in object.tracks %}
+                <tr>
+                    <td>{{rank}}#1</td>
+                    <td>{{track.title}}</td>
+                    <td>{{track.scrobble_count}}</td>
+                    <td>
+                        <div class="progress-bar" style="margin-right:5px;">
+                            <span class="progress-bar-fill" style="width: {{track.scrobble_count|mul:10}}%;"></span>
+                        </div>
+                    </td>
+                </tr>
+                {% endfor %}
+            </tbody>
+            </table>
+        </div>
+    </div>
+</div>
+<div class="row">
+    <div class="col-md">
+        <h3>Last scrobbles</h3>
+        <div class="table-responsive">
+            <table class="table table-striped table-sm">
+            <thead>
+                <tr>
+                    <th scope="col">Date</th>
+                    <th scope="col">Track</th>
+                    <th scope="col">Album</th>
+                </tr>
+            </thead>
+            <tbody>
+                {% for scrobble in object.scrobbles %}
+                <tr>
+                    <td>{{scrobble.timestamp}}</td>
+                    <td>{{scrobble.track.title}}</td>
+                    <td>{{scrobble.track.album.name}}</td>
+                </tr>
+                {% endfor %}
+            </tbody>
+            </table>
+        </div>
+    </div>
+</div>
+{% endblock %}