Make migrations_path to support multiple migration paths

[renepardon]

I use the nWidard Modules package in multiple projects and this spatie/laravel-settings looks like a good addition. But I want to separate the settings to every module including the migrations. For this use-case I want to be able to configure multiple paths to settings-migrations because each module should be responsible for their own settings.
Right now you can just use one path which defaults to database/settings

[renepardon]

#92