Changed spelling of Metadata plus extended locations

[m8pple]

In the v4 spec the element name is Metadata, and that was used in the example xml given
to Andrew. But in the orchestrator it is given as MetaData. Depending on how much xml
is floating around with the MetaData form, we could just change the spec to say that
either form is correct?

I also notice the grammar allows the meta-data to be attached to lots of different
elements, which was true of v3 and earlier, but in the v4 discussion it was required
that it only be attached to GraphType or GraphInstance, and nowhere else.

I'm happy to open it up, as it is a non-breaking change, and I didn't really get the
reasoning for restricting it in the first place.

[m8pple]

An actual bug is that in the v4 grammar the elements have to be in a strict order,
and it was specified the MetaData comes before Properties:

https://github.com/POETSII/poets_improvement_proposals/blob/2a355282f3aa3912bdacf4ec50bf25199bdf310d/proposed/PIP-0020/virtual-graph-schema-v4.rnc#L238-L255

In the orchestrator grammar they are switched:

Orchestrator/Config/V4Grammar3.ocfg

Lines 4 to 6 in b5615c3

	<GraphType GraphType="[1],[1]id">
	<Properties Properties="[0..1]"><CDATA CDATA="[1]"/></Properties>
	<MetaData MetaData="[]"/>

[m8pple]

The orchestrator grammar also doesn't include the key and value attributes, so rather than:

<Metadata Metadata="[]"/>

it should be:

<Metadata Metadata="[],[1](key,value)"/>

[m8pple]

Fixed by this commit: 74e2747

[heliosfa]

We are happy to revert to the specified case ("Metadata") as we don't currently do anything with it.

[m8pple]

I've rebased the proposed patch from last month into #264 , as it is still a blocking issue.

[heliosfa]

Resolved in #264