[Xesam] Need paged search mode for xesam

[Jamie McCracken]

For a serch gui its essential to page results using an offset and limit
to define the page size

currently xesam api lacks the offset component (although it has a limit)

there are several workarounds:

1) add a hit.offset property 
2) add new api : GetPagedHits (in string search, in int PageStart, in
int PageEnd, out aav results) or similar
3) add a hit.pagesize property and have GetNextpage/getPrevPage methods

Anyway we desperately need this to make things fast otherwise putting a
huge result set over dbus is gonna be awfully slow

jamie