Fix ol externs definitions

* Namespaces must be defined;
* Interfaces must be initialized.
Fix namespacing convention
Hide the rotate control when the rotation is 0

To prevent the cursor to be displayed as a pointer (only happens with bootstrap)
Add 'tooltip'-tag to KML example.

Fixes #2708.
Merge pull request #2782 from fredj/hide-rotate

Hide the rotate control when the rotation is 0
Merge pull request #2784 from marcjansen/tag-kml-example

Add 'tooltip'-tag to KML example.
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
Remove unused ResetRotation name attribute
Use a standard title attribute for the control buttons
Add missing 'button' type attribute to html button