CommitView: Allow changing of context size

This adds a slider in the commit view with
which the user can change the context size.

This is useful for example if the hunks are too
big; by changing the context size, a hunk can be
split and then the changes can be committed.

html/views/commit/commit.css

@@ -48,6 +48,18 @@ table.diff {
 	margin-top: 30px;
 }
 
+#contextSize {
+	width: 80px;
+	margin-top: -0.5px;
+	float: right;
+	margin-right: 20px;
+}
+
+#contextTitle {
+	margin-right: 3px;
+	float: right;
+}
+
 .diff a.stagebutton {
 	display: block;
 	width: 40px;