PLT-4535/PLT-4503 Fix inactive users in searches and add option functionality to DB user search (#4413)

* Add options to user database search

* Fix inactive users showing up incorrectly in some user searches

* Read JSON for searchUsers API into anonymous struct

* Move anonymous struct to be a normal struct in model directory and upadte client to use it

* Added clarification comment about slightly odd query condition in search

model/user_search.go

@@ -0,0 +1,39 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"io"
+)
+
+type UserSearch struct {
+	Term           string `json:"term"`
+	TeamId         string `json:"team_id"`
+	InChannelId    string `json:"in_channel_id"`
+	NotInChannelId string `json:"not_in_channel_id"`
+	AllowInactive  bool   `json:"allow_inactive"`
+}
+
+// ToJson convert a User to a json string
+func (u *UserSearch) ToJson() string {
+	b, err := json.Marshal(u)
+	if err != nil {
+		return ""
+	} else {
+		return string(b)
+	}
+}
+
+// UserSearchFromJson will decode the input and return a User
+func UserSearchFromJson(data io.Reader) *UserSearch {
+	decoder := json.NewDecoder(data)
+	var us UserSearch
+	err := decoder.Decode(&us)
+	if err == nil {
+		return &us
+	} else {
+		return nil
+	}
+}