add possibility to remove reward vatriable or unlist at value 0

[LucienBreitkopf]

As a DM, I want to only see reward variables that are actually being used or have a value.
This might be especially important if a variable is no longer used and now just lingers there wit 0 vaue, menacingly...

Example:

@(Samson) Mia 5.12.33, Your dm rewards:
rewards - 0 <-- THIS
dmrewards - 1200

[LucienBreitkopf]

Another (preferred) option could be instead of listing reward variables, "just" list the reward pool, since that is the relevant part for a DM.
The variables are tech babble and never used by the actual user.

So instead of this:

@(Samson) Mia 5.12.33, Your dm rewards:
bonusRewards - 777
dmrewards - 1200

Show this:

@(Samson) Mia 5.12.33, Your reward pools:
dm - 1977