Instruct iD to load gpx file

When one clicks on the edit link of an uploaded GPX file, this instructs
the iD editor to load the respective GPX data from the appropriate URL.

See https://github.com/openstreetmap/iD/issues/970#issuecomment-43439476.
Replace <bdi> and </bdi> with Unicode markers in titles
Wrap the ID in <bdi> tags for RTL locales
Qualify SCALE in tests
Remove bogus sort that is implied by the intermate association
Update to iD v1.3.10
Modified changeset#read to use xml builder, to be fixed to pass tests, added comments to read xml view
Merge branch 'master' into changeset_comments
Updated changeset xml builder, controller and tests