+ Add in SelectCell, kev/value functionality

Changes in SelectEditor, fixes undesirable sort by key, added key/value properties.

Main reason for this change is re-sorting SelectEditor items by key (id).
E.g. { 1:"Basic", 3:"C", 6:"C#", 5:"Java", 2:"Pascal", 4:"Python" } (sorted by name) 
becomes \[Basic, Pascal, C, Python, Java, C#\] (sorted by id/year).

Another reason is reusability. Developer can reuse object and specify key/value properties.
E.g. 
var langs = [
{id:1, year:1964, name:"Basic"},
{id:3, year:1972, name:"C"},
{id:6, year:2000, name:"C#"},
{id:5, year:1995, name:"Java"},
{id:2, year:1970, name:"Pascal"},
{id:4, year:1991, name:"Python"}
];
handsontable({
  columns: [{
	  editor: 'select',
	  selectOptions: langs,
	  selectKey:"id",
	  selectText:"name"
	}]
});

This way, elements will not be sorted again by id, backend is in charge for sorting!

In HOT documentation http://handsontable.com/demo/selectEditor.html, only array is officially supported. This change also supports arrays.There is no backward compatibility issues.