Search Improvements 2.17.6

• Require XF2.1+
• Rework "Allow empty search" support, support for XF2.1.8+ features and also XF2.1.0+

• Add missing phrase for admincp user change log

• Do not apply content weighting which skips content types for content type specific searches

• Fix search breaking when a user could see all forums, and setting content weighting was set to 0 to exclude that content type from search
• Setting content weighting to 0 now excludes a content type for all sort orders, not just relevency

• Fix ElasticSearch x2/v5 compatibility

• ElasticSearch v5 compatibility fix for content type weighting in search results

• A content type weighting of zero now correctly excludes that content type from results

• Fix that * was injected for member-like searches

• Fix content weighting values being clamped to 0 or 1
• Fix "Allow empty search" to work as expected without ElasticSearch Essentials installed

• Only apply content weighing if more than 1 content type is permitted to be returned in a search query