All operators which changes tracking data now just tags dopsheet as outdated,
actual re-calculaiton of happens only when this information is actually needed
(like on dopesheet draw).
This makes things a bit faster when there's no dopesheet visible in current
screen and also makes it much easier to update dopesheet using dependency
graph.
Also renamed dopesheet_sort_order to dopesheet_sort_method in rna and internal
stuff which makes much more sense and also correlated with naming in
file browser.
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