Move touchstart preventDefault to ol.renderer.dom.Map

`preventDefault` is called to prevent the img context menu on mobile devices.
Add ol.renderer.dom.Map#disposeInternal
Merge pull request #2855 from fredj/blur_preventDefault

Move touchstart preventDefault to ol.renderer.dom.Map
Add uriScheme parameter to Bing Maps metadata request to avoid mixed content
Merge pull request #2864 from bartvde/bing-mixed-content

Avoid mixed content in Bing Maps (r=@elemoine)
Cluster source calls loadFeatures on vector source

Closes #2801
Merge pull request #2866 from elemoine/2801

Cluster source calls loadFeatures on vector source
Add old value to property change events
Merge pull request #2865 from elemoine/oldvalue

Add old value to property change events
Make "map" a property of ol.control.Control
Update the custom-controls example

Update the custom-controls example to show how to custom controls can be notified (and take action) when the control is added to, and removed from, the map.