Add the possibility to normalize/standardize a layer's attribute

Addressing https://bugs.launchpad.net/oq-svir/+bug/1253013 and https://bugs.launchpad.net/oq-svir/+bug/1253011

3 algorithms implemented (ranking, z-scores, min-max) and accessible through a register. To add a new algorithm it's sufficient to implement it and to add it to the register.