the module should manage the contents of extensions.lua and extensions.ael

[lelutin]

the default contents of "extensions.lua" on debian can interfere with what's configured in extensions.conf. the default contents from "extensions.ael" seems a bit less problematic by default since it doesn't look like it's defining extensions, but it should still be cleared out by default.

the module should have parameters that make it possible to deploy content for those two files.