provenance text update

Hi Felix,
Here's that provenance text update where I've:
- made some wording updates on the description
- renamed the data category, actually just to provenance (the provRef 
aspect amkes it slightly broader than just agents)
- removed the trans/transRev subdivision and introduced a 
differnetiating flag 'activity'. Currently this just has values 
translation and translationRevision, but we can quickly add to this as 
suggested by marcis
- made the use of pointer and non pointer rules mutually exclusive 
(hopefullly examples will now tell us which we really need)
- allow stand off provenance records to be used in global _and_ local
- I broadened the language for the provRef attribute, so it can still 
point to a PROV record (specifically an entity one), but could also 
point to other records. Seeing the work starting on XML change records 
at TPAC and also seeing some convergence on a specific PEMT activity 
logging format in XML between CNGL and the CASMECAT project - it seemed 
prudent not to exclude these others (note this isn't bound to the 
activity value like the other attributes)

Note, I didn't yet update the attribute names in the notes on pointer 
with html usage.

Later Tuesday I'll aim to get you the informative annex on PROV usage - 
I was just updating the content Dom provided to give the turtle rather 
than the native text version of examples - I think that will make it 
more relevant for the HTML and SemWeb crowd.

Then I'll start on reworking the examples, to make them more realistic, 
and to remove pointer/non-pointer mixes.

thanks for your patience on this,
cheers,
Dave