[Rev 14] RFR: WIP: 8236651: Simplify and update glass gtk backend

[Thiago Milczarek Sayao]

> This proposed change does the following:
> 
> - Ports DND target to use GTK reducing code size and adding extra text / image formats (such as .gif);
> - Use gtk signals instead of gdk events (also to reduce code size);
> - Simplifies geometry (sizing/positioning) with a more straightforward code (less special cases) ;
> - Replaces (pointer and focus) grabbing with a gtk approach;
> - Reworked frame extents (the wm extension to get decoration sizes) to reduce size and complexity;
> - Simplified cursor changing;
> - Reduced the use of gtk/gdk deprecated functions;
> - Removes Applet/Web Start code;
> - Fixes https://bugs.openjdk.java.net/browse/JDK-8237491;
> 
> In general it reduces code size and complexity and hands more work to gtk.
> 
> ![image](https://user-images.githubusercontent.com/30704286/71791073-58779d00-3012-11ea-89e5-07588f7a41cc.png)

The pull request has been updated with a new target base due to a merge or a rebase.

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Commits:
 - 694641f6: JDK-8236651 Simplify and update glass gtk backend
 - 9397a748: Merge pull request #4 from openjdk/master

Changes: https://git.openjdk.java.net/jfx/pull/77/files
 Webrev: https://webrevs.openjdk.java.net/jfx/77/webrev.14
  Stats: 3361 lines in 12 files changed: 777 ins; 1802 del; 782 mod
  Patch: https://git.openjdk.java.net/jfx/pull/77.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/77/head:pull/77

PR: https://git.openjdk.java.net/jfx/pull/77