Add mcp_forum_actions_before/after events

Adds two events:

mcp_forum_actions_before
mcp_forum_actions_after

These events show up in styles/prosilver/template/mcp_forumhtml, before

<fieldset class="display-actions">

and after

</fieldset>

For my QTE extension, i need to set a attribut for severals topics, so i need a custom combobox for that.