Stat allocation: don't show stat options in Reward create/edit screens

[saraolson]

When you set your stat allocation method to be based on task activity, you shouldn't be able to make a reward associated with a stat. so we need to hide that control.

only habits, dailies, and todos can affect the training stat for that allocation method.

[dinesh-thiyagarajan]

I can pick this up

[saraolson]

@dinesh-thiyagarajan Hi there! If you're still interested in taking this on, you're welcome to pick it up.