Add Mattermost Desktop 4.5.0 (#1959)

* Add Mattermost Desktop 4.4.2

* Change folder name to one without spaces in it

* Removed space from id

* Add Mattermost Desktop 4.5.0

manifests/Mattermost/MattermostDesktop/4.5.0.yaml

@@ -0,0 +1,15 @@
+Id: Mattermost.MattermostDesktop
+Version: 4.5.0
+Name: Mattermost Desktop
+AppMoniker: mattermost
+Publisher: Mattermost
+License: Copyright (c) 2016-present Mattermost, Inc.
+LicenseUrl: https://github.com/mattermost/desktop/blob/master/LICENSE.txt
+Tags: chat, collaboration, irc, work, teams
+Description: Mattermost Desktop application for Windows
+Homepage: https://mattermost.com/
+Installers:
+  - Arch: x64
+    Url: https://releases.mattermost.com/desktop/4.5.0/mattermost-desktop-4.5.0-x64.msi
+    Sha256: 4e81e1dc79668722fec14960723950446f2d941fd6b9642d4770868c4bed21c6
+    InstallerType: msi