This addresses warnings from Clang-Tidy's `readability-else-after-return`
rule. This should be the final commit of the series of commits that
addresses this particular rule.
No functional changes.
Function names will be updated in a separate commit.
This will be the place for the new particle system and other
code related to the Simulation data block. We don't want
to have all that code in blenkernel.
Approved by brecht.
