Add buttons to allow loading of incomplete diffs (#16829)

This PR adds two buttons to the stats and the end of the diffs list to load the (some of) the remaining incomplete diff sections.

Contains #16775
    
Signed-off-by: Andrew Thornton <art27@cantab.net>


## Screenshots

### Show more button at the end of the diff
![Screenshot from 2021-09-04 11-12-37](https://user-images.githubusercontent.com/1824502/132091009-b1f6113e-2c04-4be5-8a04-b8ecea56887b.png)

### Show more button at the end of the diff stats box
![Screenshot from 2021-09-04 11-14-54](https://user-images.githubusercontent.com/1824502/132091063-86da5a6d-6628-4b82-bea9-3655cd9f40f6.png)

1 files changed, 2 insertions, 0 deletions

diff --git a/web_src/js/index.js b/web_src/js/index.js
index e6269c8abf..74aca6913b 100644
--- a/web_src/js/index.js
+++ b/web_src/js/index.js
@@ -27,6 +27,7 @@ import {initNotificationsTable, initNotificationCount} from './features/notifica
 import {initLastCommitLoader} from './features/lastcommitloader.js';
 import {initIssueContentHistory} from './features/issue-content-history.js';
 import {initStopwatch} from './features/stopwatch.js';
+import {initDiffShowMore} from './features/diff.js';
 import {showLineButton} from './code/linebutton.js';
 import {initMarkupContent, initCommentContent} from './markup/content.js';
 import {stripTags, mqBinarySearch} from './utils.js';
@@ -2881,6 +2882,7 @@ $(document).ready(async () => {
   initFileViewToggle();
   initReleaseEditor();
   initRelease();
+  initDiffShowMore();
   initIssueContentHistory();
   initAdminUserListSearchForm();