[Rev 04] 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;
> 
> 
> In general it reduces code size and complexity and hands more work to gtk.
> 
> Important notice: As I could not test the code for handling web start and web applets because browsers do not support it anymore and java has removed "javaws", I took the liberty to remove the code. Will restore if necessary.
> 
> ![image](https://user-images.githubusercontent.com/30704286/71791073-58779d00-3012-11ea-89e5-07588f7a41cc.png)

The pull request has been updated with 1 additional commit.

-------------

Added commits:
 - cc7745b4: Pass more tests

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/77/files
  - new: https://git.openjdk.java.net/jfx/pull/77/files/49426b66..cc7745b4

Webrevs:
 - full: https://webrevs.openjdk.java.net/jfx/77/webrev.04
 - incr: https://webrevs.openjdk.java.net/jfx/77/webrev.03-04

  Stats: 57 lines in 2 files changed: 11 ins; 30 del; 16 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