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/lann/builder/README.md

@@ -0,0 +1,68 @@
+# Builder - fluent immutable builders for Go
+
+[![GoDoc](https://godoc.org/github.com/lann/builder?status.png)](https://godoc.org/github.com/lann/builder)
+[![Build Status](https://travis-ci.org/lann/builder.png?branch=master)](https://travis-ci.org/lann/builder)
+
+Builder was originally written for
+[Squirrel](https://github.com/lann/squirrel), a fluent SQL generator. It
+is probably the best example of Builder in action.
+
+Builder helps you write **fluent** DSLs for your libraries with method chaining:
+
+```go
+resp := ReqBuilder.
+    Url("http://golang.org").
+    Header("User-Agent", "Builder").
+    Get()
+```
+
+Builder uses **immutable** persistent data structures
+([these](https://github.com/mndrix/ps), specifically)
+so that each step in your method chain can be reused:
+
+```go
+build := WordBuilder.AddLetters("Build")
+builder := build.AddLetters("er")
+building := build.AddLetters("ing")
+```
+
+Builder makes it easy to **build** structs using the **builder** pattern
+(*surprise!*):
+
+```go
+import "github.com/lann/builder"
+
+type Muppet struct {
+    Name string
+    Friends []string
+}
+
+type muppetBuilder builder.Builder
+
+func (b muppetBuilder) Name(name string) muppetBuilder {
+    return builder.Set(b, "Name", name).(muppetBuilder)
+}
+
+func (b muppetBuilder) AddFriend(friend string) muppetBuilder {
+    return builder.Append(b, "Friends", friend).(muppetBuilder)
+}
+
+func (b muppetBuilder) Build() Muppet {
+    return builder.GetStruct(b).(Muppet)
+}
+
+var MuppetBuilder = builder.Register(muppetBuilder{}, Muppet{}).(muppetBuilder)
+```
+```go
+MuppetBuilder.
+    Name("Beaker").
+    AddFriend("Dr. Honeydew").
+    Build()
+
+=> Muppet{Name:"Beaker", Friends:[]string{"Dr. Honeydew"}}
+```
+
+## License
+
+Builder is released under the
+[MIT License](http://www.opensource.org/licenses/MIT).