Allow ApplicationTransaction comments to be edited and deleted

Summary:
Allows you to edit or delete comments in appplications which support ApplicationTransactions.

UI/UX stuff:

  - The dialogs are rough but I want to do a dialog design pass more generally, @chad has some mocks.
  - When you add new mentions via edit, they don't currently count as mentions. I'm not sure what I want to do about this.
  - When you edit or delete a comment, we do not publish any notifications about it. I think this is reasonable.
  - I didn't separate "delete" out versus "edit"; I assume it will be reasonably intuitive that deleting all the text deletes effectively deletes the comment. I also want to discourage deletion somewhat (we still show the transaction, just show that the comment has been deleted).

Test Plan:
Transaction view, note "Edit" and "Edited" links:

{F26914}

Edit view, has some design issues but I want to do a pass on dialogs in general:

{F26915}

History view:

{F26913}

Reviewers: vrana, btrahan, chad

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1082

Differential Revision: https://secure.phabricator.com/D4149

src/view/AphrontDialogView.php

@@ -16,6 +16,7 @@ final class AphrontDialogView extends AphrontView {
   private $width      = 'default';
   const WIDTH_DEFAULT = 'default';
   const WIDTH_FORM    = 'form';
+  const WIDTH_FULL    = 'full';
 
   public function setUser(PhabricatorUser $user) {
     $this->user = $user;
@@ -115,6 +116,7 @@ final class AphrontDialogView extends AphrontView {
 
     switch ($this->width) {
       case self::WIDTH_FORM:
+      case self::WIDTH_FULL:
         $more .= ' aphront-dialog-view-width-'.$this->width;
         break;
       case self::WIDTH_DEFAULT: