boost 6.x-1.19-beta1

This is the first release of Boost 6.x-1.x since 1.18 was released, more than two years ago. Since then, the dev version had evolved, but no formal release had been made.

Recent changes include:

* #886450: Crawler not working with path prefix language negotiation by edjay/hedac
* #1544032: remove useless translations of the empty string by mvc
* #1053190: DELETE FROM Syntax in boost_crawler_prune_table by fivefrank
* #1350416: Fixes for PHP warnings by Lars Toomre
* #1171594: Notice: Undefined offset: 1 in _boost_get_menu_router() [boost.module] *FIX* by Peter Bowey
* #1056578: Allow for a domain whitelist/blacklist setting. by cotto
* #1219484: Types application/xml and application/json not supported (support for services module) by sitiveni

There are also countless improvements and fixes by Mikeytown2.

Please help review the issue queue and test the module! At the moment of this writing, there are 157 open bug reports (139 for 6.x-1.x) and 299 support requests. Help find duplicate issues, or support requests for which we should write a handbook page.