Remove white spaces from the key used to index into the client id's

In function 'win_menu()' we 'rsrtip' the 'win_str' variable, we also need to do the same in 'i3clients()' for 'win_str'.

Else it does not allow us to choose window who name end with white spaces. 
Ex : u'[9:Workspace] Synaptic Package Manager  '