Switch actant role (at the background) based on entity type valency

[davidzbiral]

When an Action is already filled in in a statement, assist users by selecting actant role for them based on valency frame (with notification) when they are selecting the actant through suggester or DnD-ing it from somewhere. This should work in a similar way as with the use of a proptype which is not in the user’s default language for Statements.
If the entity type of the newly added actant is not allowed by the valency frame (entity type valency) for subject, then make it a1 if allowed for a1; if not even for a1, make it a2; if for neither, make it a pseudo-actant (and display the usual warning of non-match with valency frame). Display notification about this change.

If the Action is added later, then do not apply this retroactively to the actants already added. Only perform the operation after at least one action is filled in. In case of valency frame mismatch in statements with 2+ actions, don't perform this operation and leave it as "s".