Deskbar: Resizable tray

* Adds max width and height arguments to
  instantiate_deskbar_(item|entry).
* Old applications just stay with a 16x16 scaled icon, though.
* All used apps within the repository are converted to the new call
  besides the input_server input method icon (that will need further
  API changes in the input_server).

Change-Id: I29cc439396917be2c24135888459d31364997dff
Reviewed-on: https://review.haiku-os.org/656
Reviewed-by: waddlesplash <[email protected]>

headers/os/interface/Deskbar.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2009, Haiku, Inc. All rights reserved.
+ * Copyright 2006-2018, Haiku, Inc. All rights reserved.
  * Distributed under the terms of the MIT License.
  */
 #ifndef	_DESKBAR_H
@@ -56,6 +56,8 @@ public:
 			bool				HasItem(int32 id) const;
 			bool				HasItem(const char* name) const;
 			uint32				CountItems() const;
+			float				MaxItemWidth() const;
+			float				MaxItemHeight() const;
 
 	// Item modification methods
 			status_t			AddItem(BView* archivableView,