Add MCP core events to allow to create more quick moderation options

Identifier: core.modify_quickmod_options
Location: mcp.php, under the default case of the switch ($action) structure.
Explanation: this event allows extensions to create custom quickmod options.

Identifier: core.modify_quickmod_actions
Location: mcp_main.php, with creating the default case for the switch ($action) structure.
Explanation: this event allows extensions to handle custom quickmod options created with the above mcp.php event.

Use case: Extensions which would need to get into MCP quickmod feature.