Introduce DefaultExperiment tag in OspSystemStructure.xml

[eidekrist]

Let's continue the discussion from #333, where @markaren proposed to introduce a DefaultExperiment tag in OspSystemStructure.xml:

My comment about putting the (optional) runtime specific entries into a DefaultExperiment tag were never addressed. I'd really like to see something like:

<DefaultExperiment startTime="0.0">
      <Algorithm name="fixedStep" stepSize="1e-4"></Algorithm>
</DefaultExperiment>

Which can be completely ommited btw, rather than:

<StartTime>0.0</StartTime>
<BaseStepSize>1e-4</BaseStepSize>
<Algorithm>fixedStep</Algorithm>

However, the parameters to the Algorithm would be algorithm specific, dunno how that should best be handled. Probably some annotations stuff. Then basically you can have the exact same layout in SSP.

[markaren]

Thanks.

It follows that I would want to make a similar change to our SSP implementation. The standard itself suggests that algorithm specific stuff like stepSize should/could be listed as annotations within SSPs DefaultExperiment tag. I suggest we do just that.

Edit: See PR #426

[markaren]

I propose to use this XML:

<DefaultExperiment startTime="0.0">
    <osp:Algorithm>
        <osp:FixedStepAlgorithm baseStepSize="0.01"/>
    </osp:Algorithm>
</DefaultExperiment >

This is quite similar to the SPP version, but without the annotation tags.

Looks better than

<StartTime>0.0</StartTime>
<BaseStepSize>1e-4</BaseStepSize>
<Algorithm>fixedStep</Algorithm>

no?