add ability to keep tracks

[ripienaar]

Not sure how this will look, clearly cant load 100s of tracks and show them on the map like we do points.

So maybe something like a special kind of point that indicates a track is there that then open a page detailing the track is a good starting point

[ripienaar]

the trails.io app uses the mid point of the route - just the track point that's the middle - and puts there a car/bike/hiking icon. This works quite well and we should do similar reusing the existing types.

We have a :points array, so a new :tracks array would be good, something like:

:tracks:
- :title: Malaga to Gordoba
  :type: :car
  :comment: road trip from Malage to Gordoba
  :date: ....
  :href: track:tracks/malaga-gordoba-20150206.gpx
  :lon: -4.420941999999968
  :lat: 36.7176291

ie. it's just a normal point instance with an additional behaviour for the href field - which could also be used to parse urls like wiki:Foo etc