Use regular points field as a fallback

[JDGrimes]

Suggested in #7 (comment):

Maybe we should look at the static points more like a fallback for when the dynamic points can't be calculate though. Of course, that doesn't make sense in every situation, since in some cases the arg it is based on will always have a usable value. Other times, however, an arg may be optional or something. So perhaps we do want to do this.

[JDGrimes]

I was just thinking, what will happen when this module is deactivated/uninstalled? Actually, I guess fallback could make this problem worse rather than better, depending upon the situation. If the points were just set to zero, then upon deactivation the reactions would just essentially be disabled (although note, that as we pointed out somewhere, it wouldn't be completely disabled because reversals would still occur). If there was a fallback though, that is, if the regular points were set to a non-empty value, then the reaction would continue to work, it just wouldn't be dynamic anymore.

(We should probably consider how we can better handle reactions in the UI that have issues with their settings, but that is an upstream issue.)

[JDGrimes]

We could just disable these reactions on deactivation, see WordPoints/wordpoints#470. Probably also the user should be notified of this when it happens.

[JDGrimes]

However, for the more general case of when an arg is optional, I think this may have some merit. it is true though that sometimes the user may just want the reaction to not award points at all if the arg in question is not set. But in that case, I suppose that they could just set the points to 0.

All things considered though, in the end it might be better to have a dedicated field to use as a fallback, instead of re-purposing this field.