Adds support for more than just text messages in the message action:

<message fade-in="0.5s" stay="1s" fade-out="0.5s">
  <text>Text to show in chat</text>
  <title>Text in title</title>
  <subtitle>Text in subtitle!</subtitle>
  <actionbar>Message above hotbar</actionbar>
</message>

They can be specified as attributes too just like text was before:

<message text="Text in chat" title="Title" subtitle="Subtitle text" actionbar="actionbar"/>

At least one of the 4 formatted-text properties is required for message action, fade in, stay and out are optional, they default to the vanilla defaults after a reset (10 ticks or 0.5s, 70 ticks or 3.5s, and 20 ticks or 1s).

The PR has been tested and works as intended.