The goal of this patch is to ensure that:
- in default placements, specials have no unique ids
- in actual placements as stored by CUI, they do
- we reset the counter for those unique ids on reset.
- we re-number specials when building an area (like on startup, or when resetting),
ensuring that the actual nodes always match the placements for a given area.
- we force saves after resetting, to ensure that the gNewElementCount is always persisted correctly.
This last part will also fix bug 1393661
MozReview-Commit-ID: HAS5J5ZSgB5
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extra : rebase_source : df62441169e07fb94e39f68a2b3e43f6ed7f464c
