Zoom button behavior improvements

[mmadia]

This is a meta-ticket, based on the ​Programming with S&T mailing list thread from June-2011

One of Haiku's attractive features is the consistency and cohesiveness of the system as a whole, including the GUI. There are a few instances where the zoom button is less than consistent (or rather, its per-application use is less than ideal).

Currently, three possible behaviors can be seen and alternate between the current dimensions and one of:

1. "best fit in minimal space" (Tracker, Mail)
2. maximized window, allowing Deskbar's menu button to be viewable (Terminal, StyledEdit, Pe)
3. full screen, no window decor nor Deskbar viewable (Web+, ShowImage, MediaPlayer)
4. remove GUI elements (Magnify, PoorMan)

The purpose of this button is to be able to switch between two meaningful window sizes. What exactly this is, is completely up to the application, and hence the different behaviour in different apps.

To note, toggling full screen is normally done with CMD+Enter. Double-clicking the content area (ShowImage, MediaPlayer) and F11 (WebPositive) are also used in some instances.