Added support for multi_fields on the Browser Tab

Title is self-explanatory.  This partially addresses https://github.com/mobz/elasticsearch-head/issues/9 and I plan on addressing it elsewhere in the coming days/weeks, depending on time.

If a multi_field is selected, sub selections are created that can be opened up themselves.  If a multi_field has a subfield with the same name as the multi_field, simply a text box is displayed, along with the other sub fields.  For example, if I've got the following multi_field with one unanalyzed field for sorting
<pre>
"phone" : {
                "type" : "multi_field", 
                "fields" : {
                    "phone" : { "type" : "string" },
                    "untouched" : {
                        "include_in_all": false, 
                        "index": "not_analyzed", 
                        "type": "string",
                        "null_value" : "￮",
                        "_comment" : "We reallt want null values to be shown last, so I'm putting in this value"
                    }
                }                
            }
</pre>
then if you click on "Phone" in the browser it expands with an input box and another expandable item for "phone.untouched". "phone.untouched" can then be expanded according the appropriate type of the subfield. This should work for nested multi_field(s), as well.