fix(image): support centered div and adjusted aligned groups

The current image component can only be centered with img element. It is not able
to center when using a different HTML element, for example, an image link with
anchor tag or a DIV container.

This PR would support to center the image not only for img tag, but also for other
HTML element by using `centered` flag.

This PR would also support to display the group images horizontally center. Additionally
the group images can now share the same vertical alignment as `top`, `middle` or `bottom`
together or can have it's own vertical alignment.

Closes: #1608

Author: ko2in

src/definitions/elements/image.less

@@ -91,27 +91,36 @@ img.ui.image {
     Vertical Aligned
   -------------------*/
 
-  .ui.top.aligned.images .image,
   .ui.top.aligned.image,
   .ui.top.aligned.image svg,
   .ui.top.aligned.image img {
     display: inline-block;
     vertical-align: top;
   }
-  .ui.middle.aligned.images .image,
   .ui.middle.aligned.image,
   .ui.middle.aligned.image svg,
   .ui.middle.aligned.image img {
     display: inline-block;
     vertical-align: middle;
   }
-  .ui.bottom.aligned.images .image,
   .ui.bottom.aligned.image,
   .ui.bottom.aligned.image svg,
   .ui.bottom.aligned.image img {
     display: inline-block;
     vertical-align: bottom;
   }
+  .ui.top.aligned.images .image, 
+  .ui.images .ui.top.aligned.image {
+    align-self: flex-start;
+  }
+  .ui.middle.aligned.images .image, 
+  .ui.images .ui.middle.aligned.image {
+    align-self: center;
+  }
+  .ui.bottom.aligned.images .image, 
+  .ui.images .ui.bottom.aligned.image {
+    align-self: flex-end;
+  }
 }
 
 & when (@variationImageRounded) {
@@ -250,11 +259,18 @@ img.ui.image {
 }
 
 & when (@variationImageCentered) {
-  .ui.centered.images,
   .ui.centered.image {
+    display: block;
     margin-left: auto;
     margin-right: auto;
   }
+  .ui.centered.images {
+    display: flex;
+    flex-direction: row;
+    flex-wrap: wrap;
+    align-items: stretch;
+    justify-content: center;
+  }
 }
 
 /*--------------