Tidies keyboard shortcut dialogs and updated cursor styles

Reorganizes the keyboard shortcut list for change view with smaller
groups of shortcuts. Also tidies up the dialog for the diff view a bit.

Updates the style for the selected line in the diff view and fixes the
focus when the diff expand/collapse buttons are activated. The scroll
behavior is changed slightly.

Change-Id: I8e520f725f4706aaad6e8bd8b99dd0e274d2f830
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
index 7595bb2..e4603b8 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
@@ -43,13 +43,15 @@
       .section {
         background-color: #eee;
       }
-      .diff-row.target-row {
-        outline: .2em solid #ddd;
-      }
       .diff-row.target-row.target-side-left .lineNum.left,
       .diff-row.target-row.target-side-right .lineNum.right,
       .diff-row.target-row.unified .lineNum {
-        background-color: #ccc;
+        background-color: #BBDEFB;
+      }
+      .diff-row.target-row.target-side-left .lineNum.left:before,
+      .diff-row.target-row.target-side-right .lineNum.right:before,
+      .diff-row.target-row.unified .lineNum:before {
+        color: #000;
       }
       .blank,
       .content {
@@ -72,9 +74,6 @@
       .canComment .lineNum[data-value] {
         cursor: pointer;
       }
-      .canComment .lineNum[data-value]:before {
-        text-decoration: underline;
-      }
       .canComment .lineNum[data-value]:hover:before {
         background-color: #ccc;
       }