Possibility of Life Respects Stellar Lifetimes

If system couldn't have existed long enough for life to form (based on one of its stars being too massive), there will be none, if it has, life will be scaled accordingly to the time it could have had to develop.
Also removed explicit checks for star types - those cases are either handled automagically by mass check (hot, massive stars), or are no longer checked for (life around white and brown dwarfs is considered unlikely and requiring rather special circumstances to form but *NOT* impossible).
Merge commit '381d452f63031af6cc5495feb0409782d06ed329'
Merge pull request #3015 from corundscale/Life_Fix

Life Emergence Respects Stellar Lifespans
Update Changelog.txt
Merge branch 'master' of https://github.com/pioneerspacesim/pioneer