Query builder (#10104)

* add query builder to facilitate dynamic SQL construction

* leverage query builder to refactor user store

This is partially setup work for MM-13120, but merged to master to avoid
further conflicts.

* fix unrelated unit test breakage

* documentation tweaks

* Apply suggestions from code review

Co-Authored-By: lieut-data <jesse.hallam@gmail.com>

* prefer comma separated case options to fallthrough

* vendor github.com/Masterminds/squirrel and deps

* switch to using github.com/Masterminds/squirrel

* rm querybuilder

vendor/github.com/Masterminds/squirrel/go.mod

@@ -0,0 +1,9 @@
+module github.com/Masterminds/squirrel
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/lann/builder v0.0.0-20180802200727-47ae307949d0
+	github.com/lann/ps v0.0.0-20150810152359-62de8c46ede0 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/testify v1.2.2
+)