[Composer] Bump guzzlehttp/guzzle to version 7 to suppress deprecation notices

- Bump divineomega/password_exposed to version 3 to remove dependency on Guzzle version 6
- Add new ICanHandleHttpResponses->getBodyString method to solve inheritance mismatch with GuzzleHttp\Psr7\ResponseInterface->getBody return type

src/Network/HTTPClient/Capability/ICanHandleHttpResponses.php

@@ -97,10 +97,9 @@ interface ICanHandleHttpResponses
 	/**
 	 * Getter for body
 	 *
-	 * @see MessageInterface::getBody()
 	 * @return string
 	 */
-	public function getBody();
+	public function getBodyString();
 
 	/**
 	 * @return boolean