"State Layer" to hold initial conditions and snapshots

[tclose]

From discussion at the NineML Standards meeting:

In addition to the parameters defined in the user layer the complete state of model will be defined in a "state layer". States would be defined per component for the components that have states (we are thinking dynamics and plasticity components at this stage), which could look something like

<ComponentState name="initialConditions">
  <ComponentReference url="http:/foo/bar.xml">PyramidalCell</ComponentReference>
  <StateValue name="v">
    <Quantity units="mV">
      <SingleValue>-65</SingleValue>
    </Quanity>
  </StateValue>
  <InRegime>Refactory</InRegime>
  ...
</ComponentState>

This state layer can then be used either to represent the initial conditions of a simulation or save a snapshot of a simulation at a particular point in time.

[tclose]

syntax follows parameterisation layer (see #41) with State substituted for Properties and for dynamics:

<DynamicsState>
  <InRegime>regimeName</InRegime>
  <StateValue name="v" units="mV">
    <SingleValue>-65</SingleValue>
  </StateValue>
  <Annotations>
      <SomeRandomTag xmlns="www.nest-simulator.org">
        <RandomVariableSeed>0000010</RandomValueSeed>
      </SomeRandomTag>
  </Annotations>
</DynamicsState>

<ProjectionState name="projState">
  <SourceState>
    <PortConnectionState port="incomingSpike">
      <EventTimes>
        <ExternalArrayValue url="saved_state.h5" columnName="incomingSpike" ...>
      </EventTimes>
      <EventValue name="value1">
        <ExternalArrayValue url="saved_state.h5" columnName="value1Values" ...>
      </EventValue>
    </PortConnectionState>
  </SourceState>
</ProjectionState>

[NineML-Committee]

The Committee approves the above approach