migrate should update/call all installers

What about having an ApplicationInstaller? with something like:

<?php

class ApplicationInstaller extends AkInstaller
{
    function up_1()
    {
        $this->runInstallers('AdminPlugin 1, Category 1, Chapter 3');
    }

    function down1()
    {
        $this->runInstallers('AdminPlugin 0, Category 0, Chapter 0');
    }
}

?>

That way you can have decoupled installers (plugins....) and have the freedom to choose which versions to install and the priority.

Then we can implement a runInstallers('all up/down') if we don't mind the priorities or versions.