Add deletion of Imgur uploads

[tipa]

Bug Report

Current Behavior
When using the Imgur image upload, those files cannot be deleted any more
Currently, this is not implemented:

upload/src/Adapters/Imgur.php

Lines 81 to 93 in e8e7f9f

	/**
	* In case deletion is not possible, return false.
	*
	* @param File $file
	*
	* @return File|bool
	*/
	public function delete(File $file)
	{
	// TODO: Implement delete() method.
	return false;
	}

The Imgur deletion API for anonymous image uploads (as used in this plugin) requires the deleteHash, which is returned upon image upload

At the moment, the plugin does not store this value:

upload/src/Adapters/Imgur.php

Lines 64 to 72 in e8e7f9f

	// successful upload, let's get the generated URL
	if ($response->getStatusCode() == 200) {
	$meta = Arr::get(json_decode($response->getBody(), true), 'data', []);
	$link = Arr::get($meta, 'link');
	$file->url = $link;
	$file->remote_id = Arr::get($meta, 'id');
	}

Expected Behavior
Users (or at least admins) can delete images that have been uploaded using the Imgur integration

Environment

• Flarum version: 1.8.8
• Extension version: 1.5.5

Possible solution(s)
I don't know the internals of this plugin, but maybe the deleteHash could be stored in the remote_id instead of the id (unless the remote_id is used for some other purpose):

upload/src/Adapters/Imgur.php

Line 71 in e8e7f9f

$file->remote_id = Arr::get($meta, 'id');

Additional Context
Related issue: #290