smw.Query add getLink() method (Special:Ask link)

Generates similar output as in SMW\QueryResult::getLink()

## Usage
var link = new smw.Query(
	printouts,
	parameters,
	conditions ).getLink();

Set caption by using parameters.searchlabel or .getLink( '...' )

Used in srf.formats.datatables() to generate export links to other
formats such a JSON, CSV without the need for corresponding PHP
function in Ajax.

$.param( {} ) ensures correct encoding (see [1])

## QUnit
+ Add tests

[1] http://api.jquery.com/jQuery.param/

Change-Id: I1957236bcd4e41428f363515d1dde888232342ff
Merge "smw.Query add getLink() method (Special:Ask link)"