Implementation part1 of multicolumn sorting feature request(1507)

I plan on implementing the feature request in 3 parts. My idea is to not
break any existing code but to build on top of it. This part that I have
written lets the user select multiple columns by pressing and holding shift
key while clicking on columns. Once the user is done selecting all the columns
this generates and redirects to a URL that is just a modified url generated
by the existing one column sorting feature. I have tested this in chrome and
firefox manually.

Part 2 will be to generate visual cues to show the sorted columns and in part 3
I will implement any tests that might be required.

Signed-off-by: Aditya Sastry <ganeshaditya1@gmail.com>