speed-up listCells('object')

	cacheAllObjectsAttributes() executes an overweight SQL request to
	fetch all attributes, used dict items, chapter names and so on. It
	is called each time the listCells('object') is called to generate the
	{$attr_X_Y} auto tags.

	Now the much lighter query in cacheDictAttrValues() is used. It
	fetches all the information generateEntityAutoTags() needs to
	calculate auto tags.

	In my environment (~8k objects) the running time of listCells('object')
	reduced from 3.9s to 1.3s after applying this change.
new hook generateEntityAutoTags

	This allows user to generate custom auto-tags
generateEntityAutoTags: clarify comment