Add changes file for 5.5.0 release

Change-Id: I4d7f809aa3938394fe8bc9e54263b5f166dddf7a
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>

dist/changes-5.5.0

+Qt 5.5 introduces many new features and improvements as well as bugfixes
+over the 5.4.x series. For more details, refer to the online documentation
+included in this distribution. The documentation is also available online:
+
+  http://doc.qt.io/qt-5/index.html
+
+The Qt version 5.5 series is binary compatible with the 5.4.x series.
+Applications compiled for 5.4 will continue to run with 5.5.
+
+Some of the changes listed in this file include issue tracking numbers
+corresponding to tasks in the Qt Bug Tracker:
+
+  https://bugreports.qt.io/
+
+Each of these identifiers can be entered in the bug tracker to obtain more
+information about a particular change.
+
+****************************************************************************
+*                           General                                        *
+****************************************************************************
+
+ - Fixed several instances of missing, incorrect or obsolete information.
+ - Updated platform-specific documentation for embedded Linux, Windows,
+   WinRT, Android, and QNX.
+ - Updated getting started information and added a topic for getting
+   started with Qt Quick Controls.
+ - Added documentation and links for the new modules on Qt 5.5
+ - Marked Qt WebKit, Qt Declarative (Qt Quick 1) and Qt Script modules
+   deprecated.
+ - Improved documentation on porting from Qt 4 to Qt 5.
+ - Updated license documentation for 3rd party libraries.