Replace table by a tree in import WMS

This PR :

 - replaces the table by a tree (infinite number of levels)
 - displays error message and input  in red when file loading failed.
 - displays an error message when the layer can't be added (no name  or no CRS)
 - optimizes the code to reduce number of digest cycles

Test [here](http://mf-geoadmin3.dev.bgdi.ch/dev_wms/)

- [x] wait for translations


Some WMS are broken see #1829