Investigate use of Global instead of Persistent

Currently we only use `Nan::Persistent` which requires that we call `Reset()` prior to the objects destruction or the object will never be garbage collected. `Nan::Global` is an alternative that provides automatically calls reset at the time of destruction of the hander.

Start by locating the uses of Nan::Persistent and reviewing how each object is destroyed. Compare those lifecycles with Nan::Global's automatic reset behavior. Done means determining whether the usages can safely switch without leaving objects uncollected, and documenting or implementing the resulting change.

Written by the indexing model from the issue text.