Fix ol externs definitions

* Namespaces must be defined;
* Interfaces must be initialized.
Fix namespacing convention
Use valid mediatype for GPX export.
Merge pull request #2792 from pgiraud/gpx_export_chrome

Use valid mediatype for GPX export.
Merge pull request #2795 from gingerik/externs

Externs
Re enable rotation button transition

The opacity transition was broken with #2782