multiple database with --pw-stdin (#2916)

* Updated utilities to unlock KDBX with OS password manager on macOS and Linux
* Use a static stream on stdin for --pw-stdin otherwise buffer loss eliminates subsequent passwords
* Update INSTALL requirements

src/cli/Utils.cpp

@@ -163,7 +163,7 @@ namespace Utils
             return password;
         }
 
-        TextStream in(STDIN, QIODevice::ReadOnly);
+        static TextStream in(STDIN, QIODevice::ReadOnly);
 
         setStdinEcho(false);
         QString line = in.readLine();