Return the option of adding slots to daily document powerup

In the previous versions, it was possible to add slots to the Daily Document powerup that would then appear inside any individual Daily Document (see https://forum.remnote.io/t/remnote-templates-vs-text-templates/1203/6). The value of having the same set of slots automatically applied to daily docs is fairly obvious.

In case the change has something to do with protecting powerups from user interference, there should be a separate powerup rem for Daily Document Slots (by analogy with the Document Sidebar for customisation).