Description and title elements

[nuest]

Add svg description and title elements, e.g.

title = "GEO label - a metadata visualisation"
description = "A GEO label representation for metadata documents "

See http://www.w3.org/TR/SVG/struct.html#DescElement

The description elements can also support basic provenance (if the request was GET) by adding the URL to retrieve the label.

<svg:svg id="NA" height="200" width="200" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:svg="http://www.w3.org/2000/svg" version="1.1">

    <svg:title>GEO label</svg:title>
    <svg:description>A visual and interactive summary for geospatial metadata.
        This document was created by the GEO label API at http://geolabel.net/ and can be retrieved via the URL: 
        http://geolabel.net/api/v1/geolabel?metadata=http://sensorweblabe.net/example/hydrophone.xml
    </svg:description>
    <svg:svg viewBox="0 0 200 200" preserveAspectRatio="xMinYMin meet">
        <svg:g transform="scale(0.8)" id="size_group" class="size_group">

<!-- rest of label -->

Or als an element of metadata to make it accessible via XPath:

<svg:svg id="NA" height="200" width="200" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:svg="http://www.w3.org/2000/svg" version="1.1">

    <svg:title>GEO label</svg:title>
    <svg:description>A visual and interactive summary for geospatial metadata.
        This document was created by the GEO label API at http://geolabel.net/ and can be retrieved via the URL: 
        http://geolabel.net/api/v1/geolabel?metadata=http://sensorweblabe.net/example/hydrophone.xml
    </svg:description>
    <svg:metadata>
        <labelUrl>http://geolabel.net/api/v1/geolabel?metadata=http://sensorweblabe.net/example/hydrophone.xml</labelUrl>
        <metadata>
            <sml:PhysicalSystem gml:id="ExampleHydrophone1">
<!-- full metadata document -->
            </sml:PhysicalSystem>
        </metadata>
        <feedback />
        <parent_metadata />
        <parent_feedback />
    </svg:metadata>
    <svg:svg viewBox="0 0 200 200" preserveAspectRatio="xMinYMin meet">
        <svg:g transform="scale(0.8)" id="size_group" class="size_group">

<!-- rest of label -->