Implement GPX parser (read/write).

Implement a parser for GPX which supports read and write.
address review by @fredj
make feature info work on touch devices for gpx example see #727
Write support for ol.parser.GeoJSON

Also add some convenience with static read and write methods based on the
singleton.
Merge pull request #732 from bartvde/geojson-write

Write support for ol.parser.GeoJSON (r=@tschaub)
fix typo in WMTS parser
Merge pull request #2 from fredj/fid

Store the KML Placemark identifier
Merge pull request #733 from ahocevar/fid

Store the feature's commonly used id. r=@fredj,@bartvde
Add parser.jsdoc file for docs on parser options.

Pointer by @ahocevar in #735
Merge pull request #736 from bartvde/jsdoc2

Add parser.jsdoc file for docs on parser options (p=@ahocevar, r=@bartvde)
FeatureId support in GML (r/w) and KML (w)

Now that we have FeatureId support (see #733), we can add this back to the
GML parsers (v2 and v3). Also add write support for FeatureId in KML, read
support was already added by @fredj
Sort exported properties
Export constrainResolution and constrainRotation from ol.View2D
Merge pull request #741 from fredj/export-view-constraints

Export constrainResolution and constrainRotation from ol.View2D
Merge pull request #737 from bartvde/feature-id

FeatureId support in GML (r/w) and KML (w) (r=@fredj)
Merge pull request #725 from bartvde/gpx

Implement GPX parser (read/write). (r=@fredj)
Dispatch an error on Geolocation failure