New symbology: add scale dependent vector rendering

[lutra]

This feature should work like this:

Let the user define different symbology in different scale intervals. In not defined scale intervals two options should be available: apply a user defined symbology or leave the vector with no symbology (transparent).

If possible, it would be great if this scale based symbology can have an option to work as "class based" and not "layer based", in a way to avoid to describe many times the classes that have the same symbology in all/many scale intervals.

[jef]

duplicate of #1727