[Qt] optimize PNG files

- provide a python script
- add optimized png files

contrib/devtools/optimize-pngs.py

@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+
+import os
+import sys
+import subprocess
+
+#optimize png, remove various color profiles, remove ancillary chunks (alla) and text chunks (text)
+#pngcrush -brute -ow -rem gAMA -rem cHRM -rem iCCP -rem sRGB -rem alla -rem text
+
+folders = ["src/qt/res/movies", "src/qt/res/icons", "src/qt/res/images"]
+basePath = subprocess.check_output("git rev-parse --show-toplevel", shell=True).rstrip('\n')
+totalSaveBytes = 0
+
+outputArray = []
+for folder in folders:
+    absFolder=os.path.join(basePath, folder)
+    for file in os.listdir(absFolder):
+        extension = os.path.splitext(file)[1]
+        if extension.lower() == '.png':
+            print("optimizing "+file+"..."),
+            file_path = os.path.join(absFolder, file)
+            fileMetaMap = {'file' : file, 'osize': os.path.getsize(file_path), 'sha256Old' : subprocess.check_output("openssl dgst -sha256 "+file_path, shell=True).rstrip('\n')};
+        
+            pngCrushOutput = ""
+            try:
+                pngCrushOutput = subprocess.check_output("pngcrush -brute -ow -rem gAMA -rem cHRM -rem iCCP -rem sRGB -rem alla -rem text "+file_path+" >/dev/null 2>&1", shell=True).rstrip('\n')
+            except:
+                print "pngcrush is not installed, aborting..."
+                sys.exit(0)
+        
+            #verify
+            if "Not a PNG file" in subprocess.check_output("pngcrush -n -v "+file_path+" >/dev/null 2>&1", shell=True):
+                print "PNG file "+file+" is corrupted after crushing, check out pngcursh version"
+                sys.exit(1)
+            
+        
+            fileMetaMap['sha256New'] = subprocess.check_output("openssl dgst -sha256 "+file_path, shell=True).rstrip('\n')
+            fileMetaMap['psize'] = os.path.getsize(file_path)
+            outputArray.append(fileMetaMap)
+            print("done\n"),
+
+print "summary:\n+++++++++++++++++"
+for fileDict in outputArray:
+    oldHash = fileDict['sha256Old'].split("= ")[1]
+    newHash = fileDict['sha256New'].split("= ")[1]
+    totalSaveBytes += fileDict['osize'] - fileDict['psize']
+    print fileDict['file']+"\n  size diff from: "+str(fileDict['osize'])+" to: "+str(fileDict['psize'])+"\n  old sha256: "+oldHash+"\n  new sha256: "+newHash+"\n"
+    
+print "completed. Total reduction: "+str(totalSaveBytes)+" bytes"