static - maintain the existing URI parameters when add "login"

This now manage the following possible URI:

* mapfishapp/
* mapfishapp/?

that will give mapfishapp/?login, and

* mapfishapp/?lang=fr
* mapfishapp/?lang=fr&

that will give mapfishapp/?lang=fr&login

Taken from OpenLayers urlAppend function
Merge pull request #476 from georchestra/issue175

static - maintain the existing URI parameters when add "login" - fixes #175