[FIX] `ilTreeAdminNodeAddedObjective` database instance

[thibsy]

Hi folks,

I noticed trunk cannot be fresh installed at the moment due to a failed setup objective ilTreeAdminNodeAddedObjective. The issue occurs because the database instance is not properly populated in the total abomination ($DIC) and cannot be service-located when creating an instance of the ilTree using $DIC->database() somewhere.

I fixed this by populating an instance of the pimple container and isolate it for this objective only, by reseting the state after the objective is achieved. The same thing is done in many other objectives.

Kind regards, @thibsy