Initial update to use NML v2beta3

Updating to v1.3.0
Merge branch 'master' into development

* master:
  Update README.md
Moving LEMS examples to relect positions in laste NeuroML2 repo

Using beta3 as LATEST_SCHEMA
Update to latest schema & Channels.xml from development nml2 repo
Using latest comp type defs from main nml2 repo
Updating to latest comp type definitions from main nml2 repo
Updated to latest nml2 schema

Adding example of exporting Property in <annotation> element
Using latest comptypes from main nml2 repo
Latest comp type defns from main nml2 repo
Adding some iaf cell base types
Copying latest example from neuroml2 repo
Updating examples & comp type defns to latest from main NML2 repo
Latest comptype defns and examples from main nml2 repo
Latets schema & examples from nml2 repo
Ditto
Updating to latest example from main nml2 repo
Latets Channel.xml from main repo
Allowing multiple child segments in morphology

It's not used correctly in LEMS, but may work for multicomp cells when
there is a uniform cond density for all channels
Changing Kohm to kohm in standard units
Using latest channels.xml & schema from main nml2 repo