Retain existing URL parameters across different view types

A new method ```update_url_parms``` has been added to retain existing URL parameters in the request query string. This method is currently being called while setting the urls for some of the UI components like toolbar buttons and paging controls.
The main function of this method is to update the URL parameters based on the UI control type while retaining the existing parameters (with the exception of a few) at the same time.
This should address some of the issues related to routing errors or code crashes due to the absence of certain URL parameters.

Other than this change, a missing route for 'download_data' was added as well.

https://bugzilla.redhat.com/show_bug.cgi?id=1130223
One of the main goals here is to use a common method for setting the url string that we set for UI components.
The ```update_url_parms``` method is used in 2 places so far -
a) L1527 where the first input parameter is a String
b) In the paging controls view where the input parameter is a Hash

Therefore while writing this method, I had to consider both cases (string and hash).
In case of a hash the first parameter can be a nil but in case of a string it cannot, hence the extra check on L1527.
However, let me look into it if I can structure the method better.