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/delete_ctx.go

@@ -0,0 +1,27 @@
+// +build go1.8
+
+package squirrel
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/lann/builder"
+)
+
+func (d *deleteData) ExecContext(ctx context.Context) (sql.Result, error) {
+	if d.RunWith == nil {
+		return nil, RunnerNotSet
+	}
+	ctxRunner, ok := d.RunWith.(ExecerContext)
+	if !ok {
+		return nil, NoContextSupport
+	}
+	return ExecContextWith(ctx, ctxRunner, d)
+}
+
+// ExecContext builds and ExecContexts the query with the Runner set by RunWith.
+func (b DeleteBuilder) ExecContext(ctx context.Context) (sql.Result, error) {
+	data := builder.GetStruct(b).(deleteData)
+	return data.ExecContext(ctx)
+}