Added support for `:skip_merge_gwt_dependencies` parameter in GWT addon.

This makes it possible to avoid adding GWT dependencies to the project
directly and thus the associated POM. This will be required to support
GWT3.x and GWT2.x simultaneously as well as making it easier to manage
dependencies in the POMs.
diff --git a/CHANGELOG b/CHANGELOG
index 63d2b20..ffaccb5 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -2,6 +2,10 @@
 * Fixed:  The fix that allowed special characters in usernames and passwords was only partially applied
           in the `1.5.6` release. The complete fix that correctly decoded usernames and passwords before
           passing them to HTTP library is now been applied.
+* Change: GWT Addon: Added support for `:skip_merge_gwt_dependencies` parameter that makes it possible to
+          avoid adding GWT dependencies to the project directly and thus the associated POM. This will be
+          required to support GWT3.x and GWT2.x simultaneously as well as making it easier to manage
+          dependencies in the POMs.
 
 1.5.6 (2018-05-10)
 * Fixed:  Ensure that the username and passwords declared for repositories are correctly url encoded for
diff --git a/addon/buildr/gwt.rb b/addon/buildr/gwt.rb
index 4e4610e..7c29667 100644
--- a/addon/buildr/gwt.rb
+++ b/addon/buildr/gwt.rb
@@ -274,8 +274,10 @@
         Buildr::GWT.dependencies(version).each do |d|
           a = artifact(d)
           a.invoke if a.respond_to?(:invoke)
-          project.iml.main_dependencies << a unless !project.iml? || existing_deps.include?(a.to_s)
-          project.compile.dependencies << a unless existing_deps.include?(a.to_s)
+          unless options[:skip_merge_gwt_dependencies]
+            project.iml.main_dependencies << a unless !project.iml? || existing_deps.include?(a.to_s)
+            project.compile.dependencies << a unless existing_deps.include?(a.to_s)
+          end
           additional_gwt_deps << a
         end