IE 11 compatibility, use Selection.collapse/extend instead of Selection.setBaseAndExtent (#1386)
IE 11 compatibility, use Selection.collapse/extend instead of Selection.setBaseAndExtent (#1386)

* IE 11 compatibility, use Selection.collapse/extend instead of Selection.setBaseAndExtent

* lint

* use collapse/extend for both forward and backward selection

* lint

* use of Selection.extend if supported

* IE11 selection compat

* cleanup

* clean up IE 11 compat code

ianstormtaylor/slate,ashutoshrishi/slate,ianstormtaylor/slate,isubastiCadmus/slate