Full Chef 11 compatibility update.

This PR adds full Chef 11+ compatibility:

* Vendor missing `chef/solr_query/*` classes (only added to load path if running in Chef Solo 11+)
* Install `treetop` gem if missing (determined by LoadError). This will not occur on Chef 10.x.
* `search` and `data_bag` methods are now part of `Chef::DSL:: DataQuery` (previously they were part of `Chef::Mixin::Language`).
* Fully backward compatibility with Chef 10.x.

See the individual commits for in depth messages/explanation.