Fix filtering aliases with non-empty sort options

Fixes #2816
Terminate early when no terms left in the suggest string.

Closes #2817
Move applying alias filter to ContextSearch#preProcess()
Date math in query_string caches now()
fixes #2808
remove the field settings for query parser cache, not really relevant
Segments API: Add version & compound for each segment
closes #2823
Fix LeastUsedDistributor and ensure random distribution for multiple non-fs directories

If we cannot determine available space the fallback scenario is now to use random distribution instead of always using the last directory.

Fixes #2820
Added sort mode to geo distance sorting. Closes #1846
Added /_plugins/ endpoint to list the names of installed plugins.