Support for other GPX fields

[IanMayo]

Some users are receiving GPX data.

The header describes it as GPX 1.1, but it includes the course and speed values that were in GPX 1.0 but not in 1.1.

We should modify our GPX importer to read in this elements.

** Note:** once we have built this, delivered it, and have confirmation that it works against client data, we'll modify Pepys-Import to load these extra fields.

Samples:

<trkseg>
   <trkpt lat="xx.xxxxxxxx" lon="y.yyyyyyyy">
      <src>2</src>
      <ele>205.7</ele>
      <time>aaaaaaaaaaa</time>
      <course>226.0</course>
      <speed>286.0</speed>
   </trkpt>
   <trkpt lat="xx.xxxxxxxx" lon=" y.yyyyyyyy ">
      <src>3</src>
      <ele>213.4</ele>
      <time>aaaaaaaaaaa</time>
      <course>226.0</course>
      <speed>286.0</speed>
   </trkpt>
   <trkpt lat="xx.xxxxxxxx" lon=" y.yyyyyyyy ">
      <src>1</src>
      <ele>175.3</ele>
      <time>aaaaaaaaaaa</time>
      <course>226.0</course>
      <speed>286.0</speed>
   </trkpt>
   <trkpt lat="xx.xxxxxxxx" lon=" y.yyyyyyyy ">
      <src>4</src>
      <ele>266.7</ele>
      <time>aaaaaaaaaaa</time>
      <course>226.0</course>
      <speed>286.0</speed>
   </trkpt>
   <trkpt lat="xx.xxxxxxxx" lon=" y.yyyyyyyy ">
      <src>5</src>
      <ele>281.9</ele>
      <time>aaaaaaaaaaa</time>
      <course>226.0</course>
      <speed>286.0</speed>