Rename all manager from nexus.* to nexus.core.*.

[MOD] Rename nexus.audio to nexus.core.audio.
[MOD] Rename nexus.database to nexus.core.database.
[MOD] Rename nexus.graphics to nexus.core.graphics.
[MOD] Rename nexus.input to nexus.core.input.
[MOD] Rename nexus.message to nexus.core.message.
[MOD] Rename nexus.resource to nexus.core.resource.
[MOD] Rename nexus.scene to nexus.core.scene.
[MOD] Rename nexus.object.base to nexus.base.object.
[MOD] Rename nexus.scene.base to nexus.base.scene.
[MOD] Rename nexus.window.base to nexus.base.window.
[DEL] Remove table.recursiveMerge().