tweaks and fixes

[gavinleroy]

• remove css class for attention elements after first render
• icon wrappers no longer change the bounding box of the node
• implication draining taints the rustc typeck variable, this was disabled so we need to figure something out there :|
• add panel of impl candidates to arbitrary proof nodes and not just failures
• place paramenv information in a monospace wrapper
• use a NestedFilter::All for the span to hirid visitor. this was the bug causing obligations to match with incredibly large spans
• misc printing minutiae
• only set projection equalities on successful goals
• stop event propagation in the hover panel

closes #26