Implement exposed actions

[Pablete1234]

Adds a way for PGM <action>s to be exposed to trigger/untrigger via commands. This is somewhat equivalent to how staff can manage monument modes via /mode start or /mode push, but for actions.

The commands to manage actions are /action or /actions, and the 3 sub-commands are list, trigger and untrigger.
/action list -> lists all exposed actions in the current match
/action trigger [action] -> triggers the action
/action untrigger [action] -> untriggers the action, keep in mind very few actions actually do anything when untriggering at all. However, it may be useful in combination with removable kits.

In order to be available to trigger by commands, actions must:

• have an id
• have the expose="true" attribute,
• support the match scope (eg: messages work too, as they work with any audience, and match is an audience) and have an id.

If you try to use expose="true" without meeting the other requirements, you'll get an XML exception with a descriptive message.

Dummy example, send a message (to everyone in the match):

<actions>
  <message id="send-message" expose="true">Chat message!</message>
</actions>

Full example, has 2 actions to start/end blitz mode. It utilizes a variable filter in blitz module, and changes the variable value in the actions, as well as broadcasting a message (could enhance it by sending a title in ).

<actions> 
  <action id="start-blitz" expose="true" scope="match">
    <message text="Blitz mode has been enabled!"/>
    <set var="blitz_enabled" value="1"/>
  </action>  

  <action id="end-blitz" expose="true" scope="match">
    <message text="Blitz mode has been disabled!"/>
    <set var="blitz_enabled" value="0"/>
  </action>
</actions>
<variables>
  <variable id="blitz_enabled" scope="match"/>
</variables>
<blitz>
  <filter>
    <variable var="blitz_enabled">1</variable>
  </filter>
</blitz>