Add a blink comparator and pixel difference to image diffs

Pixel difference uses CSS mix-blend-mode, which is supported currently
only on Firefox >= 32 and on Safari >= 7.1. Implementation is behind a
Javascript feature test.

For other browsers, there's a blink comparator.

Code changes:

* ImageDiffHandler now takes the page it's used on as argument. We need
  that to get labels. DOM generated is a
  little bit different (new controls).
  
* Diff pages adapted to new constructor of ImageDiffHandler.

* CSS and Javascript changes implementing the new controls, making use
  of two new static image resources. Since I felt that the new controls
  deserved tooltips, I also gave the opacity slider a tooltip: changed
  to <a>, and slider handle changed from <div> to <span>. CSS ensures
  everything still displays the same (basically display:inline-block).
  
* Supplied messages for English, French, and German for the new
  tooltips.

Tested on IE8, Safari 6.1.6 & 7.1, Chrome 38, FF 33.1 & FF 3.6.13

1 files changed, 2 insertions, 2 deletions

diff --git a/src/main/java/com/gitblit/wicket/pages/BlobDiffPage.java b/src/main/java/com/gitblit/wicket/pages/BlobDiffPage.java
index 71516ec8..ae737a53 100644
--- a/src/main/java/com/gitblit/wicket/pages/BlobDiffPage.java
+++ b/src/main/java/com/gitblit/wicket/pages/BlobDiffPage.java
@@ -52,7 +52,7 @@ public class BlobDiffPage extends RepositoryPage {
 		if (StringUtils.isEmpty(baseObjectId)) {

 			// use first parent

 			RevCommit parent = commit.getParentCount() == 0 ? null : commit.getParent(0);

-			ImageDiffHandler handler = new ImageDiffHandler(getContextUrl(), repositoryName,

+			ImageDiffHandler handler = new ImageDiffHandler(this, repositoryName,

 					parent.getName(), commit.getName(), imageExtensions);

 			diff = DiffUtils.getDiff(r, commit, blobPath, DiffOutputType.HTML, handler).content;

 			if (handler.getImgDiffCount() > 0) {

@@ -63,7 +63,7 @@ public class BlobDiffPage extends RepositoryPage {
 		} else {

 			// base commit specified

 			RevCommit baseCommit = JGitUtils.getCommit(r, baseObjectId);

-			ImageDiffHandler handler = new ImageDiffHandler(getContextUrl(), repositoryName,

+			ImageDiffHandler handler = new ImageDiffHandler(this, repositoryName,

 					baseCommit.getName(), commit.getName(), imageExtensions);

 			diff = DiffUtils.getDiff(r, baseCommit, commit, blobPath, DiffOutputType.HTML, handler).content;

 			if (handler.getImgDiffCount() > 0) {