PLT-4938 Add app package and move logic over from api package (#4931)

* Add app package and move logic over from api package

* Change app package functions to return errors

* Move non-api tests into app package

* Fix merge

app/session_test.go

@@ -0,0 +1,31 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"github.com/mattermost/platform/model"
+	"testing"
+)
+
+func TestCache(t *testing.T) {
+	session := &model.Session{
+		Id:     model.NewId(),
+		Token:  model.NewId(),
+		UserId: model.NewId(),
+	}
+
+	sessionCache.AddWithExpiresInSecs(session.Token, session, 5*60)
+
+	keys := sessionCache.Keys()
+	if len(keys) <= 0 {
+		t.Fatal("should have items")
+	}
+
+	RemoveAllSessionsForUserId(session.UserId)
+
+	rkeys := sessionCache.Keys()
+	if len(rkeys) != len(keys)-1 {
+		t.Fatal("should have one less")
+	}
+}