use compressed images in drupal core

Following #511114: Use smaller feed.png image to use compressed images in drupal core. Attached is a collection of compressed images (found in misc directory). Compression reports are as follow

Image	                        compressed size	Savings	% Savings

powered-blue-88x31.png	      2.05 KB	        16 bytes	  0.76%
powered-gray-80x15.png	      741 bytes	      17 bytes	  2.24%
powered-gray-88x31.png	      2.00 KB	        19 bytes	  0.92%
powered-black-135x42.png	    2.73 KB	        19 bytes	  0.67%
powered-black-80x15.png	      1.42 KB	        12 bytes	  0.82%
powered-black-88x31.png	      2.04 KB	        19 bytes	  0.90%
powered-blue-135x42.png	      2.94 KB	        18 bytes	  0.59%
powered-blue-80x15.png	      994 bytes	      17 bytes	  1.68%
menu-collapsed-rtl.png	      108 bytes	      22 bytes	  16.92%
menu-leaf.png                 137 bytes	      57 bytes	  29.38%
forum-hot-new.png	            1.28 KB	        4 bytes	    0.30%
forum-new.png	                1.11 KB	        6 bytes	    0.53%
grippie.png	                  108 bytes	      54 bytes	  33.33%
draggable.png	                262 bytes	      87 bytes	  24.93%
druplicon.png	                3.92 KB	        58 bytes	  1.42%
forum-closed.png	            1.07 KB	        5 bytes	    0.45%
arrow-desc.png	              118 bytes	      1 bytes	    0.84%