Fix warnings on non-static data member initializers (C++11 feature)

We're not formally using C++11 yet so those trigger compilation warnings
(at least with GCC 5):

./main/input_default.h:122:30: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
  CursorShape default_shape = CURSOR_ARROW;
                              ^

Note: We may allow those eventually (especially for non-int static const),
but most of current occurrences were inconsistent with all other classes.

See also http://www.stroustrup.com/C++11FAQ.html#member-init

editor/spatial_editor_gizmos.cpp

@@ -715,6 +715,7 @@ EditorSpatialGizmo::EditorSpatialGizmo() {
 	instanced = false;
 	spatial_node = NULL;
 	gizmo_plugin = NULL;
+	selectable_icon_size = -1.0f;
 }
 
 EditorSpatialGizmo::~EditorSpatialGizmo() {