[sailfish-browser] Add bookmark to launcher support

I don't think this is safe enough. 

For example I have first 
1) sailfish-browser-google-0.desktop 
2) then sailfish-browser-google-1, 
3) then I delete from grid sailfish-browser-google-0.desktop
4) then when I try to add google again wouldn't it get name sailfish-browser-google-1.desktop again and thus names would collide.

What would work would be form basename and try appending 1..n until similarly named file does not exist and return that.