ITextLink moved to ClickHandler, TextLinkPtr > ClickHandlerPtr.

Global methods textlnkOver/Down/DrawOver were replaced by
static members of ClickHandler, now global state consists
of the handler pointer + host pointer, who declares callbacks
for the active and pressed handler changed events.

This will allow to use ClickHandler from different hosts
simultaneously (like HistoryItem / BotDescription / BotKeyboard).

Not yet tested.

Telegram/SourceFiles/app.cpp

@@ -2040,8 +2040,8 @@ namespace App {
 	}
 
 	void clearHistories() {
-		textlnkOver(TextLinkPtr());
-		textlnkDown(TextLinkPtr());
+		ClickHandler::clearActive();
+		ClickHandler::unpressed();
 
 		histories().clear();