Paging in SPARQL strategy

[coreation]

tdt/formatters#11

[coreation]

@pietercolpaert @mielvds
This is now implemented in a fairly robust way. It can handle select and construct queries, AND the 2 ways of putting the mandatory where clause with the query. The where clause is mandatory, however the keyword "where" is not. In the commit you might notice something strange about the paging parameters, limit and offset, these combined cannot be greater than 10K, why? Because virtuoso (the triple store I'm currently working on) doesn't allow sorts to be more than 10K. Limit and offset is applied after sorting, thus these must be changed.

Another part I want to bring up is that some select queries, even capped at 10K trigger the arc2 to blow up (out of memory), with the query it's useless to pass along a limit and offset as we implement that in the strategy itself. However I think it should be possible to pass along a paging parameter when creating the resource that says "I want my results in pages of x".

[coreation]

#72 explains why this has to be reopened, this is afaik only fixable by configuring the virtuoso server. @pietercolpaert @marc-portier.