Admin - improve filter on indicators in numerator mapping

[olavpo]

If mapping a numerator to an indicator, only indicators with denominator = 1 should be options.

[stale]

Hi! Due to a lack of activity on this issue over time it seems to be stale. If still relevant, please provide information that moves it forward: e.g. more information, reason to keep it open, supply a pull request, etc.
Any activity will keep it open, otherwise it will be closed automatically. Thanks! 🤖

[stale]

Automatically closing due to lack of activity. 🤖