Use "user-select: none" to provide a visual cue about copy/paste JS magic

Summary:
  - For line numbers, use "user-select: none" to make them unselectable. This provides a stronger visual cue that copy/paste is enchanted.
  - In Paste, make it look sensible again after the blame-on-blame refactor in Diffusion. See also TODO to share this code formally.
  - In Diffusion, use the "phabricator-oncopy" behavior.

NOTE: I left blame/commit columns selectable in Diffusion, since you might reasonably want to copy/paste them?

NOTE: In Differential, the left side of the diff still highlights, even though it will be copied only if you select part of a line on the left and nothing else. But this seemed like a reasonable behavior, so I left it.

Test Plan:
  - Looked at Paste. Saw a nice line number column. Selected text, got the expected selection. Copied text, got the expected copy.
  - Looked at Diffusion. Saw a nice line number column, still. Selected text, got expected selection. Copied text, got expected copy.
  - Looked at Differential. Highlighted stuff, got expected results. Copied stuff, got expected results.

Reviewers: btrahan, vrana, jungejason

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1123

Differential Revision: https://secure.phabricator.com/D2242

src/applications/paste/controller/view/PhabricatorPasteViewController.php

@@ -149,6 +149,9 @@ final class PhabricatorPasteViewController extends PhabricatorPasteController {
     Javelin::initBehavior('phabricator-oncopy', array());
     $rows = $this->buildDisplayRows($text_list);
 
+    // TODO: Split the "one-up source listing" view into its own class and
+    // share it properly between Paste and Diffusion.
+
     $corpus_table = phutil_render_tag(
       'table',
       array(
@@ -183,7 +186,13 @@ final class PhabricatorPasteViewController extends PhabricatorPasteController {
           'href' => '#'.$anchor,
         ),
         $n);
-      $rows[] = '<tr id="'.$anchor.'"><th>'.$link.'</th>'.
+      $link = phutil_render_tag(
+        'th',
+        array(
+          'class' => 'diffusion-line-link',
+        ),
+        $link);
+      $rows[] = '<tr id="'.$anchor.'">'.$link.
         '<td style="white-space: pre-wrap;">'.
         // NOTE: See the 'phabricator-oncopy' behavior.
         "\xE2\x80\x8B".