Notifications preflet and notification_server

Notifications preflet:
-Use sliders instead of text fields for width and timeout
-Remove icon size choice (mini icon looks horrible)
-Consolidate both "Enable" checkboxes into one
-Fix Revert button, remove Apply button, add Defaults button
-All changes to settings saved immediately
-Live example notification message shown when settings changes are made
-Add setting for individual apps to specify whether their notifications
	should be muted
-Remove history list (to be implemented later)

BNotification class:
-BNotification records the signature and name of application that
	created it
-New functions to get source application signature and name

Notification Server:
-Notification pop up view layout fixes and bold font size fix
-Remove notifications history from AppUsage class (will be saved in
	cache instead)
-Remove vector of NotificationView objects which isn't needed
-Get source application info from notification object, not the received
	message which is not reliable

headers/os/app/Notification.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010, Haiku, Inc. All Rights Reserved.
+ * Copyright 2010-2017, Haiku, Inc. All Rights Reserved.
  * Distributed under the terms of the MIT License.
  */
 #ifndef _NOTIFICATION_H
@@ -34,6 +34,9 @@ public:
 	static	BArchivable*		Instantiate(BMessage* archive);
 	virtual	status_t			Archive(BMessage* archive, bool deep = true) const;
 
+			const char*			SourceSignature() const;
+			const char*			SourceName() const;
+
 			notification_type	Type() const;
 
 			const char*			Group() const;
@@ -73,6 +76,8 @@ public:
 private:
 			status_t			fInitStatus;
 
+			BString				fSourceSignature;
+			BString				fSourceName;
 			notification_type	fType;
 			BString				fGroup;
 			BString				fTitle;