Add-On preflet

[Numerio]

We have a very useful add-on system, so apps can load modules to extend functionality, however there's no control on add-ons, functionality such as

• Disabling add-ons
• Blacklisting add-ons
• Using different module versions

Additionally, there are a few redundant implementations of module lookup and loading in different parts of the system.

We would ideally, introduce a sort of "add-on kit" that

1. Give applications a class such as AddOnManager that allows to watch for directories and load add-ons.
2. Applications can enforce security rules
3. The Add-On preflet can automatically retrieve add-ons in the system and allow the user to manage them (as explained before).