refactor(core): optimize image loading

- JavaScript runs so fast that LQIP will never be detected
- Increase the running priority of image processing in posts

Enhancement for #1267

_sass/addon/commons.scss

@@ -71,9 +71,9 @@ a {
 img {
   max-width: 100%;
   height: auto;
-  transition: all 0.7s ease-in-out;
+  transition: all 0.35s ease-in-out;
 
-  &[data-lqip='true'] {
+  .blur & {
     $blur: 20px;
 
     -webkit-filter: blur($blur);