Add notes for refactoring ResourceItem

[manup]

The goal is to make ResourceItems as small as possible aka cache friendly, and also very fast. Currently each item results in many heap allocations and is internally not very type safe. We can do a lot better here.

The QString has the biggest impact especially for legacy code which may do hundrets of string comparisons foe each incoming APS Indication, and timestamp to string conversions during WebSocket event generation.

This PR has no code changes only comments to figure out where to go.