Deny bare trait-objects

[syberant]

So I noticed there doesn't seem to be much work going on here at the moment and figured this might be a good time to make this PR since the likelyhood of massive quantities of merge conflicts is severely reduced. If this is not the right time then feel free to close this PR and schedule these changes for another time, all changes were made completely automated by running cargo fix after adding #![deny(bare_trait_objects)] to lib.rs.

dimforge/ncollide#297 provides a bit of background for the reasons why it's preferable to enforce dyn in front of every trait-object but in short it enhances their visibility by distinguishing them from structs.

[sebcrozet]

Hi, thank you for this PR!

This is unfortunately not a good time as my comment on dimforge/ncollide#297 (comment) applies to nphysics too where massive work is also happening in the ccd branch. Sorry I did not mention nphysics in my aforementioned comment.

I'll keep this PR open for now though, just to remember that needs to be done at some point after the work on the ccd branch is complete.