Improve rules database handling

[manup]

• Only store rules than needed and on application exit.
• Fix store/reload timestriggered and lasttriggered which was always "none" previously.

[ebaauw]

I kinda liked that timestiggered and lasttriggered reset on deCONZ restart. Makes for easier checking that rules are fired; now I would need to record the values and compare them later, instead of simply restarting deCONZ and checking whether they've become non-null

[sadpixel]

Could persisiting these values across service restart be offered as an option? Maybe toggled by a new entry under /config? (Or perhaps it would make more sense as a new CLI flag…)

[manup]

Reverted the loading at startup in PR #7678 for my purpose it's enough to have the last session recorded in the database.