ol.render.DragBox renamed to ol.render.Box
Use better type
Rename a property
ol.render.Box refactoring
Add ol.interaction.DragBox
Make DragZoom interaction inherit from DragBox
Rename drag zoom interaction exports file
No default style in ol.render.Box
Add style option to DragBox interaction
Add style option to DragZoom interaction
Remove dragbox.exports
Add ol.DragBoxEvent
Make DragBox interaction dispatch events

- boxstart/boxend events are dispatched,
- behavior is removed,
- geometry drawn by box render is a simple polygon instead of one with hole.
Remove DragZoom from default interactions

As it only works with canvas renderer.
Add dragzoom example, configured with canvas renderer
Merge pull request #1422 from tonio/vector-api-dragbox

[vector-api] Refactor DragZoom