Fixed Timeline.setGroups for Array

[lewisjb]

Quote from docs: "groups can be an Array with Objects, a DataSet (offering 2 way data binding), or a DataView (offering 1 way data binding)".

However, in #2315 the array support was broken.

The specific change can be seen by comparing develop to master

The problem is groups.filter(filter), because filter is:

var filter = {
  filter : function(group){
    return group.visible !== false;
  }
}

groups should be an Array, so groups.filter is expecting a function, but is given an object. This results in Uncaught TypeError: #<Object> is not a function (to test for yourself just put [].filter({}) in your development console).

So I changed filter to be the function, and pass in {filter: filter} to DataView. I felt this was a cleaner solution than passing in filter.filter to groups.filter because the function is the shared information.