[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.

mod/hovercard.php

@@ -14,6 +14,7 @@ use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Contact;
 use Friendica\Model\GContact;
+use Friendica\Util\Proxy as ProxyUtils;
 
 function hovercard_init(App $a)
 {
@@ -96,7 +97,7 @@ function hovercard_content()
 		'name'     => $contact['name'],
 		'nick'     => $contact['nick'],
 		'addr'     => defaults($contact, 'addr', $contact['url']),
-		'thumb'    => proxy_url($contact['thumb'], false, PROXY_SIZE_THUMB),
+		'thumb'    => ProxyUtils::proxifyUrl($contact['thumb'], false, ProxyUtils::SIZE_THUMB),
 		'url'      => Contact::magicLink($contact['url']),
 		'nurl'     => $contact['nurl'], // We additionally store the nurl as identifier
 		'location' => $contact['location'],