Add "None" to draw-features example's select

This allows to deactivate drawing entirely in the example.
Correct minor typo in tasks/readme
Merge pull request #2212 from elemoine/drawinteraction

Add "None" to draw-features example's select
Merge pull request #2213 from probins/patch-1

Correct minor typo in tasks/readme
Correct code type in tasks/readme
Merge pull request #2215 from fredj/json-type

Correct code type in tasks/readme
Add ol.structs.RBush#getIterator function
Check if the tree is changed between iterator.next
Add ol.source.Vector#getFeaturesIterator function
Use goog.iter.some instead of ol.structs.RBush#forEachInExtent
Use goog.iter.filter instead of ol.structs.RBush#forEachInExtent
Remove ol.structs.RBush#forEach function
Use goog.iter.toArray instead of ol.structs.RBush#forEachInExtent
Use goog.iter.forEach instead of ol.structs.RBush#forEachInExtent
Use iterator in ol.source.Vector#forEachFeatureAtCoordinate
Use iterator in ol.source.Vector#forEachFeatureInExtent

The function now behaves like a real forEach (ignores the callback return value)
Remove ol.structs.RBush#forEachInExtent function