Automatic XmlNamespacePrefix for extension projects

[PathogenDavid]

(This issue fell out of today's DCM)

We should consider either adding a XmlNamespacePrefix to the script extension template or injecting a default one when none is present.

We also need to fix XmlNamespacePrefix for types which have no namespace. (Perhaps with an overload which omits the namespace parameter.)

We also discussed whether maybe instead of generating p1 etc namespace prefixes for unlabeled namespaces we should use the full namespace name. One concern with this is it bloats the XML with repeated namespace names. (@glopesdev Was this concern for bloating the file size or just making it annoying to manually inspect the XML?)

Something we didn't talk about: Maybe instead of generating p1 etc namespaces, could we use a hash of the namespace name instead?