Implement message action replacements

[Pablete1234]

Allows replacements being defined inside message actions. It supports a list of replacements, where the id of such replacement will be evaluated when sending the message to the audience, for the scope the action is ran on.

Example

    <trigger scope="player">
      <filter>
        <pulse period="1s" duration="0.5s" filter="some-region"/>
      </filter>
      <action>
        <set var="team_score" value="team_score+1"/>
        <message text="Ding {num}!">
          <replacements>
            <decimal id="num" value="team_score"/>
          </replacements>
        </message>
      </action>
    </trigger>

Note: Currently the only supported replacement is decimal, in the future more may come (thinking of players, teams, and durations). id is required in all replacements and it's what will get used to search for a {id} text to replace.

decimal replacement has a required value attribute, which supports formulas (eg: team_score / 100), and a format attribute, which takes in a java decimal format pattern such as #.00 (always show 2 decimal places).
Eg:
<decimal id="id" value="team_score/100" format="#.00"/>