Xfwm4: improve accessibility (wider bottom edge)

Since Xfwm have never expressed much interest in virtual resize
grips extending away from the window area, and need to support non-
composited configurations anyway, this usability fix is needed in
Numix. Single-pixel borders are not enough.

This commit adds a 5px bottom border and big corner resize grips to
Xfwm allow windows to be resized more easily. This improves matters
significantly for tablet and mouse/touchpad users.

The corner resize grips are from NeXTSTEP, or more accurately its
clones on Linux such as Window Maker. The bottom border as a whole
is styled to match the rest of the theme.

Closes numixproject/numix-gtk-theme#100.

src/xfwm4/bottom-active.xpm

@@ -1,6 +1,11 @@
 /* XPM */
 static char * bottom_active_xpm[] = {
-"8 1 2 1",
+"8 5 3 1",
 " 	c None",
-".	c #484848",
+".	c #444444",
-"........"};
+"#	c #484848",
+"........",
+"........",
+"........",
+"........",
+"########"};

src/xfwm4/bottom-inactive.xpm

@@ -1,6 +1,11 @@
 /* XPM */
 static char * bottom_inactive_xpm[] = {
-"8 1 2 1",
+"8 5 3 1",
 " 	c None",
-".	c #393939",
+".	c #444444",
-"........"};
+"#	c #393939",
+"........",
+"........",
+"........",
+"........",
+"########"};

src/xfwm4/bottom-left-active.xpm

@@ -1,6 +1,11 @@
 /* XPM */
 static char * bottom_left_active_xpm[] = {
-"1 1 2 1",
+"24 5 3 1",
 " 	c None",
-".	c #484848",
+".	c #444444",
-"."};
+"#	c #484848",
+"#.......................",
+"#.......................",
+"#.......................",
+"#.......................",
+"########################"};

src/xfwm4/bottom-left-inactive.xpm

@@ -1,6 +1,11 @@
 /* XPM */
 static char * bottom_left_inactive_xpm[] = {
-"1 1 2 1",
+"24 5 3 1",
 " 	c None",
-".	c #393939",
+".	c #444444",
-"."};
+"#	c #393939",
+"#.......................",
+"#.......................",
+"#.......................",
+"#.......................",
+"########################"};

src/xfwm4/bottom-right-active.xpm

@@ -1,6 +1,11 @@
 /* XPM */
 static char * bottom_right_active_xpm[] = {
-"1 1 2 1",
+"24 5 3 1",
 " 	c None",
-".	c #484848",
+".	c #444444",
-"."};
+"#	c #484848",
+".......................#",
+".......................#",
+".......................#",
+".......................#",
+"########################"};

src/xfwm4/bottom-right-inactive.xpm

@@ -1,6 +1,11 @@
 /* XPM */
 static char * bottom_right_inactive_xpm[] = {
-"1 1 2 1",
+"24 5 3 1",
 " 	c None",
-".	c #393939",
+".	c #444444",
-"."};
+"#	c #393939",
+".......................#",
+".......................#",
+".......................#",
+".......................#",
+"########################"};