Create an all-in-one handlebars file for Discord

[Kneckter]

This update adds a new handlebar file to the Discord templates that gives a template for each NotificationType. I was able to test the following:

• ItemAdded
• PlaybackStart
• PlaybackProgress
• PlaybackStop
• AuthenticationFailure
• AuthenticationSuccess
• SessionStart
• PluginInstalled
• PluginInstalling
• PluginUninstalled
• UserCreated
• UserDeleted
• UserLockedOut
• UserPasswordChanged
• UserDataSaved
• ItemDeleted

I was not able to trigger these to confirm their formatting:

• Generic (probably not used)
• SubtitleDownloadFailure
• PendingRestart (I tried with the restart with the plug-ins, but the server logs didn't push a notification)
• TaskCompleted (I ran some tasks but the server didn't push a notification)
• PluginInstallationCancelled (Installs were too fast to trigger this. Format should work like the other notifications)
• PluginInstallationFailed (Format should work like the other notifications)
• PluginUpdated (Installing an old version and then a new version didn't not cause an update notification. Format should work like the other notifications)
• UserUpdated (I couldn't tell how this one was triggered)

This kind of setup could also be applied to other notification providers since the if_equals helper is available to all of them.