Alteration extend should support native transformations

[Seddryck]

At the moment when creating a new column with the alteration extend the only language supported is ncalc. It should be possible to use the native language to take advantage of the native transformations but also to have an easy way to deal with dateTime columns.

<extend identifier="[base-column]">
  <script language="native">
      numeric-to-clip([min], [max])
  </script>
</extend>

[Seddryck]

Beta available at https://ci.appveyor.com/project/Seddryck/nbi/builds/27970180/artifacts or 1.21.0-beta0215