Made Common namespaces more consistent

This is a follow-up on the decision we've come to in #7036.

A lot of the traits in Common still used old RA-style namespaces. This moves them to Common.Traits.

Additionally, this moves a couple more traits from RA to Common.
It also hurts the unit with damage over time. Actually a good example on how not to code modular traits, because it has a hard-coded sprite sequence. It might make sense to split it into two (one render, one damage) trait in the future.