refactor xfwm theme

-now png based
-add borders to light theme
-add thicker bottom border for easier resizing

common/xfwm4/themerc-dark

@@ -0,0 +1,23 @@
+button_offset=2
+button_spacing=4
+
+show_app_icon=true
+
+full_width_title=true
+
+title_shadow_active=false
+title_shadow_inactive=false
+
+title_horizontal_offset=3
+
+active_text_color=#afb8c5
+active_text_shadow_color=#2f343b
+
+inactive_text_color=#808791
+inactive_text_shadow_color=#2f343b
+
+shadow_delta_height=2
+shadow_delta_width=0
+shadow_delta_x=0
+shadow_delta_y=-5
+shadow_opacity=40