[WIP] Rewrite to Proxy class: (#5507)

* Rewrite to Proxy class:
- introduced new Friendica\Network\Proxy class for in exchange of proxy_*()
  functions
- moved also all PROXY_* constants there as Proxy::*
- removed now no longer needed mod/proxy.php loading as composer's auto-load
  will do this for us
- renamed those proxy_*() functions to better names:
  + proxy_init()           -> Proxy::init()         (public)
  + proxy_url()            -> Proxy::proxifyUrl()   (public)
  + proxy_parse_html()     -> Proxy::proxifyHtml()  (public)
  + proxy_is_local_image() -> Proxy::isLocalImage() (private)
  + proxy_parse_query()    -> Proxy::parseQuery()   (private)
  + proxy_img_cb()         -> Proxy::replaceUrl()   (private)

* Ops, need to set $a here ...

* CR request:
- moved Proxy class to Friendica\Module
- extended BaseModule

* Ops, no need for own instance of $a when self::getApp() is around.

* Proxy-rewrite:
- proxy_url() and proxy_parse_html() are both non-module functions (now
  methods)
- so they must be splitted into a seperate class
- also the SIZE_* and DEFAULT_TIME constants are both not relevant to module

* No instances from utility classes

* Fixed error:
- proxify*() is now located in `Friendica\Util\ProxyUtils`

* Moved back to original place, ops? How did they move here? Well, it was not
intended by me.

* Removed duplicate (left-over from split) constants and static array. Thank to
MrPetovan finding it.

* Renamed ProxyUtils -> Proxy and aliased it back to ProxyUtils.

src/Content/ForumManager.php

@@ -10,6 +10,7 @@ use Friendica\Core\L10n;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Contact;
+use Friendica\Util\Proxy as ProxyUtils;
 
 require_once 'include/dba.php';
 
@@ -110,7 +111,7 @@ class ForumManager
 					'name' => $contact['name'],
 					'cid' => $contact['id'],
 					'selected' 	=> $selected,
-					'micro' => System::removedBaseUrl(proxy_url($contact['micro'], false, PROXY_SIZE_MICRO)),
+					'micro' => System::removedBaseUrl(ProxyUtils::proxifyUrl($contact['micro'], false, ProxyUtils::SIZE_MICRO)),
 					'id' => ++$id,
 				];
 				$entries[] = $entry;