Legend maps

[olafveerman]

Add a legend to the maps.

For the heatmap for example:

<div style="font-size: 0.8em;">
<strong>Number of occurrences</strong> - <em>Excluding false alarms</em><br/>
<ul>
<li style="background-color: #f1c40f;">&nbsp;</li>
<li style="background-color: #f39c12;">&nbsp;</li>
<li style="background-color: #e67e22;">&nbsp;</li>
<li style="background-color: #d35400;">&nbsp;</li>
<li style="background-color: #b14600;">&nbsp;</li>
<li style="background-color: #8f3900;">&nbsp;</li>
</ul><br/>
<ul>
<li class="first">0</li>
<li>10</li>
<li>50</li>
<li>250</li>
<li>750</li>
<li>1500</li>
</ul><br/>
<style type='text/css'>
li {
  display: block;
  float: left;
  padding: 0 5px;
  text-align: center;
  width: 25px;
}
li.first {
  margin-left: -17px;
}
</style>
</div>