Adds a sindex_status query.

Next step is to use it in the query language.
Adds sindex_status method to the table_t val.
Adds QL support for sindex_status and sindex_wait.
Sindex statuses seem to be sort of working.
Adds a method to get all dispatchees in the broadcaster.
In theory this makes sindex status go to all shards.
Fix some bugs with all_reads.
Refactors the unshard function and fixes a bug.

The bug had to do with using an incomplete context_t object.
In theory stores now offer post construction progress.
Fixes a few bugs in getting sindex progress.
Makes sindex status functions variadic.
Adds index status to js and py.
Adds tests for sindex status functions.
Get lines under line limit.
Fix things per code review.
Fix line lengths.
Add comment not to transpose lines.
Explicit compairson to null and indentation fix.
inner_t -> variant_t
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