Rewrite:

- moved constants GRAVITY_* from boot.php to Friendica\Model\Item
- also rewrote some array initialization:

From:
````
<?php
$arr = [];
$arr['foo'] = "FOO";
````

To:
````
<?php
$arr['foo'] = "FOO";
````
- added a few type-hints

src/Module/Api/Twitter/Statuses/NetworkPublicTimeline.php

@@ -47,7 +47,7 @@ class NetworkPublicTimeline extends BaseApi
 		$start = max(0, ($page - 1) * $count);
 
 		$condition = ["`uid` = 0 AND `gravity` IN (?, ?) AND `uri-id` > ? AND `private` = ?",
-			GRAVITY_PARENT, GRAVITY_COMMENT, $since_id, Item::PUBLIC];
+			Item::GRAVITY_PARENT, Item::GRAVITY_COMMENT, $since_id, Item::PUBLIC];
 
 		if ($max_id > 0) {
 			$condition[0] .= " AND `uri-id` <= ?";