DamageText code quality changes and new DT lifetime and accumulation lifetime cvars

Follow up to !1235 (merged)

Looking at the diff as a whole is not recommended, I separated the changes into smaller commits which are more readable.

Changed 4 space indentation to 1 tab indentation.

Line lengths are below 120 now, mostly below 100.

Formatting mostly follows Allman now instead of I think K&R.