macro: add line numbers into Python API output

[oliver-sanders]

In order to provide text editor support for Rose validation output we will need line numbers to be available via a Python API to the validate functionality.

The easiest way to do this will likely be to put this location information into the config node (metom.rose.config.ConfigNode).

Note:

1. Line numbers are already present in the function which loads the config (metomi.rose.config.load) they just aren't reflected in the config yet.
2. Check out the Language Server Protocol (LSP) docs to make sure we have enough information, we may need column numbers too.